I mean, you don't have to believe it or not.
Couple things right off the start.
Believing something to be real does not make it real. Believing something is not real does not make it not real on that same note. What's real or not real requires evidence.
The evidence we're discussing in this topic is largely subjective value based. It's a difference of opinion that cannot actually be right or wrong because of that subjective value.
I'm positive it's okay for you to think casters have it better and for me to think all classes get to participate in the adventure and have fun in different ways allowing for each class to be good in their own way. That's just different opinions. ;-)
People swore up and down that non-casters weren't in any way lesser than casters in 5.0, and yet the designers themselves later straight-up said that long-rest characters, especially casters, were outperforming non-casters in the actual feedback they were getting from real, live games. Just because it isn't a problem for you doesn't mean it isn't a problem for anyone.
People with say all kinds of things. That doesn't make them correct. This would be appealing to the masses.
IIRC, the issue was that players weren't following the encounters per day and short rests model given and that led to what you're describing so that led to changes. What casters
might have been doing is not indicative of what they
are doing now after those changes.
If it's not a problem for me and it is a problem for someone else then that also begs the question of why and what each group of players is doing differently. If the groups aren't playing how the system was meant to be played then it doesn't make sense to blame the system. Adjusting the system to compensate for how the players are playing is a possible solution and that's already been done moving into 2024 rules. Since that solution has been implemented we can no longer claim that spell casters > martials based on that feedback because the conditions have already been changed.
tldr; Feedback on 5.0 cannot be used to reflect on 2024 rules. We would need to play more 2024 rules and present opinions based on that play.
I fundamentally disagree that casters are "not good until high levels." They require slightly more optimization effort to reach their full potential, but that in no way means they're somehow bad until 11+ or whatever threshold you decide upon (since I find many who argue for such a threshold keep it quite...mobile, shall we say.) Wizards and Land Druids can be that good by level 6, doubly so because they have slot recovery mechanics.
Slot recovery cannot make them "doubly good" because they aren't doubling slots or actions in having that recovery.
You went with the wizard mainly and included the druid in your opinion. That's cherry picking as we're talking about all casters as a group and then using high end casters to represent that whole group. Wizards are not representative of all spell casters. They are, however, often considered the best and can be discussed as a representative of wizards specifically.
6th level wizards have 10 spell slots (4/3/3) and can recover 3 levels worth of spell slots on a short rest. The land druid (not just a druid but a specific subclass of druid) has the same 10 spell slots and the same spell recovery, but being a specific subclass of druid becomes even less indicative of spellcasters in general.
Fireball (Wizard, Arid Land Druids) and call lightning (any Druid) are great damage options, and you only need one other reliable damaging slotted spell (e.g. not cantrips) to have reliable damage output, e.g. magic missile (Wizard) or ice knife (Druid). Shield gives a Wizard all the in-combat defense you could ever need, to the point that Bladesinger Wizards are some of the best tanks in the game, and while Druid doesn't have anything quite that good, barkskin is still pretty solid. That's only three spells, and at level 6, a Wizard or Druid can prepare ten. Add in haste or fly for a terrifically strong buff effect (Druids would probably go with the ever-present backstop, revivify, or a spell from their subclass). And even if you did both, you'd still have half your prepared spells remaining.
I'll start with the fireball example. That wizard has 3 fireballs per day, 4 if they recover a 3rd level slot. You've also added haste and fly as options here but that wizard is still limited to those 3rd level spells. So fireball being the first priority because that was the first thing mentioned means casting 3 fireballs is pretty much casting no fly or haste spells. That wizard gets to shine for 3 actions with those spells compared to a fighter who shines almost every round in the day in comparison through extra attack, a bonus feat, weapon mastery, more hit points and AC.
Fireball can do significant total damage but still doesn't drop most 2CR+ monsters because of hit point inflation. It's normal for CR2 monsters to have 60+hp against a spell that does ~28 damage on a failed save and less when the targets do save. Those fireballs help clearing the trash while real damage dealers deal with the real threats.
Magic missile is a lower spell and does ~10 damage. But you're also using a slot for mage armor and slots for shield so that restricts either the AC benefits or the reliable damage. The wizard is likely spending arcane recovery on these slots to maintain that better. Casting magic missile 4 times per day and shield for 3 rounds is the same problem with fireball. That damage is low and that AC is temporary and it's a small part of the day compared to every round a fighter is wearing armor and doing damage all the time.
That's just combat. Some of those spell slots need to go towards social and exploration to make the claim of superiority. Duration spells are often require concentration and rituals also require concentration so those spells get dropped in exchange for other spells, or those other spells cannot be claimed to be used.
When going into a dungeon or dungeon-like space with 20-30 areas 10 spell slots plus recovery isn't all that. The "caster is better" argument comes from always having plenty of spell slots available, which is not the case.
The druid isn't doing any better. Land druids do get that slot recovery but most spell casters do not.
Barkskin lasts an hour. A day lasts 24 hours and that spell needs to be used periodically. Call lightning does ~16 damage on a failed save to multiple targets and costs concentration. Ice knife does ~12 damage to the primary target and ~7 damage to nearby targets.
This is the same problem the wizard has in that it's a few spells a few times per day and then not the rest of the day like the fighter. The druid also needs to split those spells among combat, social, and exploration pillars.
tldr; not all the slots can go to combat to make the claimed premise, the spell slots are still very limited at 6th level to cover an entire day of adventuring, and focusing on combat spells that don't do enough damage to deal with the important opponents in that combat doesn't demonstrate the superiority
I definitely think 10 spells prepared to spread across three spell levels--meaning you can have a distinct spell for every slot you have at 6th level!--is plenty to be versatile and yet also very strong. You can easily have one defensive option, one offensive option, and one other/utility option per spell level, plus an extra spell to do whatever you want with. And then Wizards are kings of ritual magic (any spell you've learned that has the Ritual tag can be cast, even if you haven't prepared it), meaning they get even more magic without needing slots to do it.
Versatility yes, but not the damage required for the combats or sustainability of using those spells yet to last. It doesn't matter if the wizard can cast 3 fireballs for the ogres in Hoard of the Dragon Queen when ogres have 68hp and fireballs do ~28 damage on a failed save.
What ritual is the wizard going to cast during an ogre fight to help?
Wizards do have many rituals, but we can't assume the wizard will have all of them by 6th level, and how much impact do those rituals actually have looking at the list?
And again, wizards having ritual adept is indicative of what wizard can do specifically and cannot be applied as a general benefit to all spellcasters.
Oh, don't get me wrong, weapon masteries are nice, especially because they're something spellcasters--even weaker ones like Warlocks--cannot get.
Weapon masteries are just an example. Fighters also get bonus feats as another example and those are very useful. I'd also take indomitable to try again on a failed save with a big bonus because a bad save can end all actions for the PC.
Rogues with reliable talent are great at skill checks. Cunning strike and weapon mastery are stackable effects. Uncanny dodge and evasion can be more useful damage mitigation than burning through spell slots.
Damage mitigation from barbarian rage is pretty useful too.
There are definite advantages to playing martial classes outside what spells can do.
But I just flatly do not accept that even relatively powerful ones like Nick, Graze, or Vex are in any way comparable even to the power of a strong 1st-level spell like shield, silvery barbs, or healing word, let alone 3rd or 4th level spells.
Why do martial classes need to cast shield at all? It's a bonus to AC when they have AC benefits before looking at weapon mastery.
A 6th level fighter in plate mail with a shield already has a 20 AC all the time. A 6th wizard who casts mage armor might have a 16 AC most of the time and a 21 AC for a couple of rounds in the entire day, and each time they cast shield they lose the opportunity to cast the magic missile that you argued.
Silvery barbs isn't in the PHB. A splat book spell that not all spell casters will have is not indicative of spell casters in general.
Healing Word? Fighters can second wind multiple times per day. Just the difference in hit die fighters and barbarians can use on a short rest adds up. Healing word is what a caster might use a limited number of times a day when something goes wrong instead of a more effective spell.
Obviously, weapon mastery properties are easier to use than these things because they just happen (though you are not quite correct, in that several of them are only 1/turn, not 1/hit, e.g. Vex, Slow, Nick, and Cleave are all once per turn).
Nick saves a bonus action so that can be another bonus action to use. That's quite good.
Vex and slow are not once per turn. Cleave is the only one that's restricted to once per turn. Vex and slow can only affect a specific target once but the martial character using these weapon masteries can apply them multiple times by attacking multiple targets. If it's the same target for some reason then TWF, or weapon swapping, or the fighter's tactical master ability can apply different weapon mastery effects with each attack; or any given attack can be replaced with the unarmed strike shove effects.
These effects can also be stacked with things like uncanny strike or battle master maneuvers.
But just because it's simple doesn't mean it's stronger.
No, just because it's simple means it's easy to use and available much earlier than those higher level spells a person might mention. It's a strong option because most weapon masteries don't have a saving throw like spells do and don't cost a limited resource like most spells do.
It really sucks to spend a spell slot and have the target save then be out of spell slots. That's not an issue with weapon masteries.
Class tiers are about potential power if you optimize, not about average performance if you presume an undefined but low level of system knowledge. Spellcasters so heavily reward making "the right" decision (or at least "a very good" decision) that their power spikes pretty hard if played to the hilt. Which...is the point of the tiers. If someone is just casually playing and doesn't really think about mechanics or optimization, then any conception of "tier list" is out the window from the get-go; you have presumed that the player generally isn't bothering to be stronger, and thus any claim that these other things are thus stronger is circular logic.
I'm not presuming characters being self limiting. I'm understanding the limitation that spell slots present. ;-)