The heart of this ancient debate comes down to the fact that most "martial"/low-magic/non-magic characters are effective in limited ways. Let's look at a level 5 Fighter (no subclass).
Why? All level 5 fighters have a subclass because subclass abilities are in the 3rd level fighter class progression like other classes.
He is effective in that he has more hit points than most other classes, can use any weapon, wear any armor, has a minor self-heal, and can grant himself an additional action in tough battles. Like most (but not all) weapon users, he can make a second attack in combat. If enemies try to push him, knock him prone, or attack his physical body, he's somewhat more resistant, and he has a few skills that can be employed. With the right weapons, he can dual wield more effectively, increase his accuracy, ensure he never fails to deal some damage, or provide limited battlefield control to those he hits.
I underlined an important part.
The reason people play fighters is because they want to play a fighter, and the class is effective at fighting.
In contrast, the level 5 Wizard has much lower hit points, few weapons, no armor and must rely solely on magic for attack and defense. However, he enjoys several at-will cantrips, which can be seen as low damage attacks (most with built-in weapon masteries!), or provide useful utility, like torchless light or being able to grasp something from a distance.
Cantrips are similar but different from weapon masteries because cantrips use the magic action and weapon masteries occur on the attack. This allows the fighter at that level to use weapon masteries 2 or 3 times on their turn as well as on another turn via reactions that might take place.
Most weapon masteries also have no saving throw, unlike most cantrips, buy they do still need to hit usually. So for something comparable like the Sap weapon mastery on a typical weapon like a longsword, mace, or morning star going with a shield style the fighter has 2 attacks and that means 2 chances to apply the effect to 1 target or 1 chance each to 2 targets where something like Vicious Mockery is all or nothing on a single target based on the DC 14 or 15 saving throw at that level.
The damage from the cantrip is far less than the longsword and landing the same effect is less reliable, and even landing damage in the first place is less reliable.
"Torchless light" is just Darkvision and anyone can run a species with it or use a hooded lantern. Or take a martial class and subclass that does grant the ability.
I think a battle master disarming an opponent from a distance with a maneuver and pushing them away from their dropped weapon in the same attack with a heavy crossbow, running up and grabbing that weapon with their movement, and then attacking that target with their own weapon that they just picked up with their second attack is way more impressive than just grabbing an object from a distance.
The 5th level fighter could be a psychic warrior instead though.
A few times per day, he can do things the Fighter cannot, such as strike multiple foes at once
5th level fighters can strike multiple foes on the attack action.
5th level fighters can do this with weapon masteries. Battle masters can add to it with combat maneuvers.
Slow, topple, and vex weapon masteries. Goading attack, menacing attack, tripping attack... combat maneuvers.
Bait and Switch, Commander's Strike, Maneuvering Attack, Rally...
protect himself from harm
Defense fighting style, Interception fighting style, Protection fighting style for themself or others in those options.
provide even greater utility
Tactical mind helps with skill checks. The battle master gains a free skill and a free artisan proficiency that can be used to brew potions during downtime with alchemist's supplies. And...
Ambush, Commanding Presence, Tactical Assessment
Wizards definitely have options here, but let's not ignore the options fighters have.
...
I once postulated the scenario of defending a small town from an oncoming horde of foes. It's possible that the Wizard could do any of the following:
If we contrive a scenario that favors a wizard of course it's going to favor the wizard.
*scout enemy positions with Fly/Invisibility/Polymorph.
Fly doesn't do much. Acquiring a flying mount does the same thing without using up concentration, and anyone can use stealth and a spyglass.
Polymorph is a bit better but tanks the PC's INT and CHA in the process.
Sneaking up and spying isn't challenging for martial characters. They can also use a disguise kit and walk through enemy encampments gathering information.
Using spells to do things with magic that mundane characters can already do isn't much of an argument. ;-)
*create arms and armor for the townsfolk with Fabricate.
That the townsfolk don't know how to use? Fighters can train people to be fighters and possibly make their own weapons. From the description:
"...You can fabricate a Large or smaller object... If you’re working with metal, stone, or another mineral substance, however, the fabricated object can be no larger than Medium... You also can’t use it to create items that require a high degree of skill—such as weapons and armor—unless you have proficiency with the type of Artisan’s Tools used to craft such objects."
Each casting of fabricate makes 1 item that the wizard needs to have the skills to make. That's a handful of objects per day at best using additional higher level slots. Assuming that wizard is actually capable of crafting those items because the base class doesn't offer that ability. A background or feat might, but most wizards don't take those IME.
Leather Armor, Hide Armor, Shields, and many weapons can each be made in a single day. The existing town artisans as a collective can already manufacture basic gear faster than the wizard spending several higher level spell slots.
What a high level martial can do that a wizard does not is maintain a small standing army in their bastion that's already geared up and trained.
*create fortifications using Wall of Stone.
From the description for wall of stone...
"The wall doesn’t need to be vertical or rest on a firm foundation. It must, however, merge with and be solidly supported by existing stone."
Wizards can only make a wall of stone where there existing stone structure to support it. This is not typical of a small town.
A fighter can, however, organize workers to log wood and build defensive structures, and / or dig trenches with wooden stakes as examples of things they can do.
In contrast, the Fighter has no bespoke abilities outside of "fight good" beyond their skills. The DM could ad hoc say that they have the ability to lead men into battle or train peasants to better fight
Martials can do things with those skills including the things I mentioned and you just agreed with.
or have advanced strategic knowledge that could develop an effective strategy for the battles (and they really should!), but they cannot match the potential versatility and power of what the Wizard might do.
Except your wizard examples really weren't very good. Skills cover scouting and spying very well, fabricate is so limited that it's not even a real argument because of the rate of item create and the need for skills and the need for the material resources in the first place, and a small town isn't likely to have those supporting stone structures in a typical setting for wall of stone.
But even if the wizard was using those options, that wizard has used up their high level spells creating defenses and cannot use those spell slots when the enemy attacks. The fighter can still fight at full strength after helping shore up defenses.
Now it's just as possible the Wizard can't do any of the above things, and is no more useful than a portable siege engine, but that's still a really good thing to have in this scenario, whereas, the Fighter, despite being a militant class, is actually not very good at killing large numbers of foes quickly.
The wizard isn't actually good at killing large numbers of foes quickly either because of hit point inflation, but also because that wizard is already using up all their high level slots per your argument to create walls of stone and equipment.
Do you think the wizard is going to ask the attackers to stop attacking so he can take a long rest when they attack while he's building fortifications? ;-)
There are, of course, many scenarios where the Fighter can outperform the Wizard.
Yep.
But there can be many more where the Wizard can do things the Fighter cannot possibly attempt.
That's not a proven statement. The limitations on spell slots exists that doesn't exist on actions in a day. It's not until tiers 3 and 4 that spellcasters become good.
This is where the disparity lies. Again, a given game might never see it, but it's not impossible either. Especially if the Wizard can begin to exert power over the world as a whole.
In the many years of playing I've never seen a wizard exerting power of the world outside of whiteroom theory and as an NPC villain plot device. This looks like hyperbole.
There can even reach a point where a hapless DM might no longer have any ability to reign in a Wizard without invoking pure fiat if they are not careful, as Gygax warned people about in the 1e DMG. Both classes can fight monsters and have their own unique role in adventuring, but the Wizard has tools which are orthogonal to the Fighter's.
Gygax didn't write these rules and we're not playing 1e. That's outdated information.
Funny thing:
A fireball alone is not fantastic. But having 5 casters starting with fireball has a significant chance of ending a fight before it really begins.
Lets assume 3 go through. 2 are saved against. That is 32d6 damage (average 112) right away.
Enough to really soften up the opposition quite heavily.
I still think you are correct. The game is better if casters and non casters synergize. And in that case, starting out with fireball is not the best option often enough. But if you are an evoker or sorcerer, you can finish an encounter with fireball very well.
Or 1 sleep spell with 4 martials gangpiling sleeping targets one at a time.
The problem isn't that fireball doesn't have uses. The problem is it takes 5 fireballs in the first place to soften up CR4-6 monsters in the first place. Spending excessive resources on damage isn't sustainable and is less efficient than using CC spells while martials use options that don't use up those resources in the same way.
In all these discussions, one thing I find notable is that I see a lot of martials in play, but I see very few non-casters.
Even the Fighters and Rogues are usually sporting some spells from something, maybe 1 in 10 PCs is actually a non-caster.
That's the epitome of anecdotal evidence. DDB stats releases has already demonstrated that non-caster fighters and rogues are more prevalent. In my case, my favorite rogue is still the thief and my favorite fighter is still the battle master, but the champion is more interesting now with the massive amount of heroic inspiration they access at higher levels.
If the spell sticks. But this is basically what I said. An option. But a mixed party is more successful.
The spell not sticking is another of the drawbacks people seem to ignore in these discussions. They always seem to be from the point of view of full resources that can be expended without caution using abilities that always stick. Typically giving scenarios catered to those abilities too.
The caster supremacy arguments seem very whiteroomy to me.