The way to fix this is to, putting it reductively, beef martials and nerf casters. For example:
I think it's important to remember that fighters and magic-users were fairly well balanced in OD&D, Basic D&D, and AD&D1e. Most of the problems in later editions (*cough* 3rd *cough*) were because they stripped away all the features that kept casters in check.
Part of that stripping away though, particularly with adding at-will spells to the mix, wasn’t so much about boosting casters (though that was the effect when things got tweaked without real consideration) as it was adjusting to the market in terms of genre imitation.
Outside of self-referential material the way fantasy treats magic has changed a LOT in the nearly 50 years since D&D came about, in the 30 since 2e came out and even in the 20 since 3e came out.
And I’ll name the elephant in the room; the single most defining system of magic in pop culture for anyone under the age of 40 is Harry Potter and it’s pretty much the opposite of Vancian resource management.
The next most is going to be any of the pop culture series focused on hidden magic people; Buffy, Charmed, the Magicians, Merlin, etc. They’re not Vancian resource management either. For that matter almost no fantasy story outside of The Dying Earth and self-referential D&D tie-ins (and not even all of them) uses D&D’s magic system.
This made D&D a horrible fit for anyone getting into gaming because of their exposure to general fantasy pop culture. You come in with ideas in your head of what you want your character to be like and, frankly, TSR D&D fought you every step of the way.m
And it didn’t just fight the spellcasters; it’s nearly impossible to create a fighter in the image of those seen on film and television, because armor played such a massive role in your ability to survive and hit points took so long to recover that their representing skill and fatigue in avoiding damage fell flat.
Outside of D&D, fantasy heroes do NOT constantly run around in plate or use shields (nor would their real world equivalents; gambesons, lighter mail shirts and brigandine would be what travelers expecting danger would wear). Maybe they get a plate armor upgrade for a big fight, but mostly fantasy heroes are depicted in what would be light or even no armor in D&D terms.
Meanwhile, you expect your starting wizard to fragile compared to a fighter; wizard as glass cannon is a known trope; what they don’t expect is that you get one pretty weak spell and then spend the rest of the adventure hiding or maybe throwing darts. Oh, if anyone hits you while you’re casting (and somehow doesn’t kill you) that one spell automatically fails.
This was another reason why, once I got driven out of D&D by my shit DM, that Palladium’s system just felt right to me. The men-at-arms’ automatic parry and higher base hit points made lighter armor not suicide (it also made spellcasters not quite so fragile).
But this failure at genre emulation is where a lot of 3e’s changes began. Armor got a max Dex bonus so agile heroes would be better off in lighter armor, spellcasters got more spells and getting them off without failure made rarer.
Then Harry Potter exploded and that’s why late 3.5e started getting at-will spell options (reserve feats) and every edition since has baked at-will spells into the classes.
My own approach was beef up fighters (not to wuxia levels, but peak human is possible to build for), and really scale down combat magic. Your default attack spells hit about as hard as a sword or bow used by a strong warrior; making combat magic more akin to an equalizer for the physically weak vs. the limited use fight enders common to D&D.
This also explains why combat magic isn’t universal because it only matches what physical prowess can achieve (particularly when the warrior wields a magic weapon) rather than eclipsing it.
There’s still big magic too, but it’s got casting times of minutes to even hours and so isn’t something you’ll be pulling out in a fight (it might be something you get into a fight to prevent someone completing though).