Undrave
Legend
This is the major difference.
Skills, improvisational actions and maneuvers that can be done at will are compared to what are supposed to be limited use clear precise mechanics (spells). This is a sensical approach as long as it is balanced correctly.
If casters are using spells as often as martials are improvising then, either the adventure is poorly designed or the game is poorly designed.
5E and modern D&D gives spell casters so much more opportunity to use magic. Compare a 1st level B/X magic user who gets 1 spell per day vs a 1st level 5E Wizard who can cast 3 spells per day (2+Arcane Recovery) + unlimited cantrips (which on their own are better than most non spellcaster actions).
In B/X the Magic User only has one time per game where they can automatically inject their agency by way of a rule (spell). Fighters can do their thing encounter after encounter and have a lot more control and agency in the game relative to the magic user.
In 5E, Wizards are empowered much further in this regard. It's a fundamental issue with the 5E game design. Wizards (and other spellcasters) are given too many tools to affect play compared to other non-caster classes.
I know a lot of people complain that magic users only get so few spells. Personally, I'm ok with it, I see the reaction to such complaint has been to push the balance too far in the other direction.
To fix this in 5E... I'd do the following.
1. Remove at-will cantrips from the game.
2. Keep the number of spells per day - but maybe cut down across the board with extra magic abilities for spell-casters.
3. Allow spell casting to be interrupted - if you are hit before your spell is cast you lose the spell (or require a Concentration save to keep the casting).
I'd look at how well classic D&D handles the balance between fighters and magic-users, and I'd implement rules to bring 5E closer in line.
I don't ACTUALLY mind most cantrips, because to me if you play a Spellcaster you want to FEEL like a Spellcaster. Having 2 spells a day or something is not being a spellcaster, it's being a diletante.
A Cantrip that does basically the same as a crossbow bolt is not really a problem. Spells that rely on attack rolls or the openent failing a saving throws are, quite frankly, the least problematic of the current system. They have uncertainty baked in.
What really matters are the spells that are basically just "Press this Button for X". "Press the Spider Climb button to climb this wall" for exemple. Instead I think it should be "Press this button to replace a Climb Check with an Arcana Check" or some other variations. Playing with casting time would also be a good idea. A lot of utility spells you'd never cast in a fight really need to take longer to use so there's a 'hook' the DM can use to make it a risk to rely only on magic.
But on the flip side the Martial classes need actual choices beyond "Which dude do I poke with my pointy stick?" you know? Even if mathematically the martial dudes can hold their own in terms of damage. It's just not interesting if you don't get to make choices that matter.
For exemple, I had this idea of a fighting style where you can apply disadvantage to your attack, provided you don't already have diaadvantage or advantage, in exchange for getting a potent debuff on the target. You don't need to track ressource but you get to choose every round wether the debuff is worth the risk of missing entirely or not.
Heck, imagine if instead of just that boring Crit Range the Champion also had: "You can apply disadvantage to your own attack provided you do not already have disadvantage or advantage, if the attack still hit, the attack is automatically a critical hit" In that case the Champion would now be in control of how hard or easy it would be to score extra damage. Big risk for big rewards.
Off course this is just the combat side of things and there's more to be had in the other pillars.
I feel like the Rogues "always a 10 or more" feature should have been more widespread. Like the Fighters should get that on their STR and CON checks or all Athletics rolls. And there was no reason to gimp the Fighters in terms of skill choice. At least give them an extra tool proficiency.
It also feels like, in general, characters should get additional skill choices as they level up that don't require them to spend a precious feat. Just to show they grow outside the Combat pillar of the game. Like at 10th level everbody gains proficiency in a skill another party member is proficient in. Might not be SUPER useful but it at least would feel interesting.