Question of efficiency
I think there is another point that is often overlooked when it comes to the martial/caster discussion. That of efficiency.
Casters are versatile but that versatility also comes with a certain amount of waste. A Spellcaster’s powers come from the intersection of prepared spells, spells slots and action economy. All involve a degree of waste. Whereas martial characters are generally tooled to do a few things very reliable and efficiently. Namely kill things and survive. Something that generally comes up a lot in D&D. A martial’s powers are reliable and convey very little waste. They are generally cumulative and make them better at what they do already. They also usually require very little action economy or lead in.
The spellcaster has to guess what spells they might need at the start of a day. Love fireball? Well if your foe happens to have fire resistance you’re a bit stuffed. Love suggestion - let’s hope they don’t have immunity to charm or that they understand your language. Sure you can have redundancy built into your choices with enough spell slots but that very redundancy is not particularly efficient. It means a big chunk of your abilities are not going to be useful in any given circumstance. Being able to change a spell after a short rest helps but only if you have an hour warning of what spell is going to be needed. Most spells act independently of each other. Very few spells make spells more effective. There are a few like mind spike but they require actions of their own and have limited effects.
Look at a fighters powers: weapon masteries, extra attacks, fighting styles, action surge, studied miss, manouvers, improved crit etc etc all making the fighter better at doing what they already do working cumulatively with each other. I also think there is a strong argument that 2024 feats boost physical attacks much more than they boost spells. No guesswork, no soul searching. In some ways 5e martial’s are far more quadratic than 5e casters.
Secondly the consumable resource of spell slots means you always have to be keeping an eye on the tank. Your most effective abilities use your higher slots which you get precious few of in a day. Arcane recovery helps somewhat but only to return the equivalent of one of your highest slots. The truth is unless your DM is formulaic/predictable: your party is happy to rest as soon as you find it convenient; and you can rest safely without interruption you can’t use your entire complement of spells without considerable risk. More inefficiency.
Martial abilities are usually unlimited by charges or if limited are rechargeable through a short rest. There are exceptions, but they are exceptions. Round after round, a martial delivers and can work at an almost peak efficiency every round.
Action economy is huge in the game. The most effective characters are able to meaningfully use an action, a bonus action and a reaction every round to maximise their utility. What reaction does a caster use every round? Shield? It takes up a prepared spell, uses a spell slot and only comes in handy if the caster happens to get hit. If your caster isn’t tooled for frontline combat then they likely aren’t going to be hit. If they’re struck by a save based effect or a high attack roll, shield doesn’t do anything for them. Similarly bonus actions spells and abilities are thin on the ground for a wizard. They are spells that grant bonus action effects but they almost all use higher level slots (3+) and need concentration, not to mention a whole action to cast in the first place. As I mentioned in my earlier post that mirror image is also going to take an action… another round gone without contributing to the fight.
When it comes to action economy a martial’s abilities generally use bonus actions or reactions (if any action at all). Off hand attack, second wind, tactical shift, action surge, weapon mastery, tactical mind, sneak attack, cunning action, rage, tactical action, manouvers, defensive duelist, improved crit, heroic warrior, savage attacker, charger, dual wielder, great weapon mastery, mage slayer, polearm mastery, Sentinel. Some of those don’t even use any action type or grant actions! The plethora of useful bonus actions and reactions makes for very efficient turns.
Lastly many spells are unreliable. Some need enemies to group together, some need friends not to be in the way. Some can be hard to cast in melee. Some can be saved against. Some come with penalties (haste). The variable length of duration for otherwise good spells makes them unreliable. Many can also be overcome simply (sleep/hypnotic pattern) and magic resistance/immunities/resistances can make them less effective. Most of all, only the ones with attack rolls get any benefit for advantage/Inspiration. All this builds more inefficiency into the system.
Whereas, hitting things with a weapon is one of the most reliable things in the game. There is an AC - which is easily outpaced by bonuses as levels scale. Advantage and inspiration both benefit this and are very easy to obtain. Very few things have resistance beyond the basic magic of weapon which is pretty much a given. No saving throws needed. No legendary resistance applicable.
As a result of these substantial changes that came about through 5e, casters benefits are overestimated and a martial’s benefits are undervalued. Skewing the martial/caster debate. 2024 seems only to have made these points more pronounced.