So back in 3e, it was noted that if your class has access to spells, it was light years better than one that didn't. Why?
It comes down to a few factors, but generally it comes down to this: spells are more powerful than most class abilities. Now you might think this is a no brainer, a limited use ability is naturally going to be better than some passive, right?
Spells are also more versatile & flexible. They have a much greater range of effects, and they can be swapped out. TSR, they could be swapped out on a daily basis. 3e, either that or cast spontaneously. 5e,
both.
And, the "limited use" of spells has always become less and less limited as you level. Again, TSR, each spell had to be memorized in advance, so unless you specifically memorized it more than one, each spell was 1/day, but you got more and more of them as you leveled, and the fallback when it wasn't worth it to use the spells was inferior weapons and attack matrixes. 3e, spontaneous casters could spam the same spell as long as they had high-enough level slots, but needed to have a metamagic feat and take a full-round action to benefit from casting in a higher level slot; wizards got scribe scroll from 1st level to expand their spell availability and wands could cheaply add many uses of a low level spell and, casters got slightly better weapons including the convenient to use at range crossbow. 5e, casters get an even better fallback in the form of at-will cantrips, some get back spells or a spell with a short rest, and all cast spontaneously, and up-casting no longer requires a feat or extra casting time - 5e.2024 even floated the idea of down-casting.
On top of that, the culture of D&D has somehow floated even closer to the 5MWD, with surveys revealing most campaign having 1-3 encounter days, with single-encounter days the most prevalent. (??? I could understand, back in the day, when you were very low level and the cleric was out of healing and you were all hurt, packing it in and resting, even if you hadn't gotten very far... but it's all so
easy, now, a short rest and you heal up without wasting the Cleric's spells, you have cantrips to use instead of slots in less important encounters, ironically, the crappy healing & concentration mechanics of 5e act as features that reduce the impulse to waste of slots. ???)
Now, I'm not saying "give all Fighters spells". I get that there's people who don't want that, and I can totally see why. But we can take a cue from spell design here and give Fighters not only more customization options, but modular ones that can be swapped out say on a long rest.
Why even a long rest, why not draw a different weapon, bring a different set of maneuvers to the party? If martials can't have powers to rival even low level spells, why not give them greater flexibility than spells?
If it doesn't seem
realistic/verysmileytoodynus to do so, well, there's no such restriction on the conceptualization of magic, so give casters far fewer slots, like 1/day at first, and 1 more per Tier after that.
I know, I know. "How is that realistic?"
While athletes, today, may focus on one sport (say, one weapon, in fencing) or even one position in their chosen sport, that's a modern thing. In the past, a knight or warrior would be expert with several weapons, for different purposes, in addition to being exceptional in other fields, as well - they were generally the upper classes, they had free time to master multiple interests.
It's also genre appropriate, heroes are frequently gifted individuals who seem to be good at anything they turn their hand too - an echo of the ancient beliefs in the innate superiority of the upper classes (OK, not that ancient, not even that old).
It's like the old school weapon specialization- you're told to make this one time decision for the rest of your career. So you become the master of the Hook Fauchard and then a few dungeon crawls later, you find this +2 Greatsword,...So you pick it up and...oh wait. You're not even proficient with it, and won't be until...let's see, you're level 4 so...ugh, level 6!? And not only that, by using this thing, your Hook Fauchard training lies fallow!
"Well, them's the breaks" the DM says. "The world doesn't change because you're in it. Who would make an enchanted hook fauchard anyways?"
It really wasn't a great weapon back in the day, but, like Ransuer was pretty amazing.
But, like, magic is supposed to be hard, right? This lifetime of study? The fighter can start play in his teens, the wiz is likely in his 30s in 1e, IIRC.
Well, in 1e, an arch-mage can "know" a minimum of 81 spells (max 171 - but it's unlikely he'd be able to
find that many), memorize 34 of them, and is proficient in 4 weapons (ironically, only 3 were usable by magic-users - UA might've added one?), the same-level fighter is proficient in 10 weapons, 9 if he took UA specialization at 1st level, 8 if that was bow spec - and that's it, no skills, no spells, no special abilities.