But is it truly something different? Because if we take away the large numbers, all it is is damage over an area. The only thing that makes it unique is pretty much the scope of what it does, but it's not inherently unique.
And that's great! A wizard/sorcerer/etc. is okay having something with larger scope. But recognize that the fighter also gets "something common" but in a larger scope as well, that being single target damage.
Just like how fireball goes to meteor swarm. A single extra attack from a fighter goes to three with added accuracy, damage, and even extra effects depending on the subclass.
Sure, that would make some sense if the Wizard's only spells were increasingly better AoE damage spells. You have the big single target damage dealer vs. the medium damage AoE. The whole point is not only do Wizard's get to AoE damage if they would like to but also can choose other ways to win at combat than damage, movement, infiltrate, gather information, etc. And these effects are even more "different" than what the Fighter can do.
Not all at once all the time sure. But combat ability and 1 or 2 of these other things is still more versatile than "big attacking damage" which is the only thing a Fighter can choose.
And the combat ability of the Wizard is close enough (and sometimes better depending on the circumstances) that it doesn't justify the Fighter getting no other major class abilites than "doing attacking damage"
In a large-scale perspective, sure. But that's only really when you flip through the spellcasting section as if all caster classes get all spells.
In reality, when you choose a class, you're fairly restricted. What you could theoretically choose doesn't matter because you can practically choose only so many spells. This is where the term Quantum Wizard comes from, which I'm sure you're familiar.
And even if you pick up every spell in your class somehow, you still can't do everything. A wizard can't heal unless they use Wish, which is a massive waste. A cleric hardly has any access to teleportation spells. A druid is vying for large AoE spells.
Wizards are utility masters, that's a fact, but their magic is often overblown when their effects actually are risky and have a large potential for failure or their effects can be acheived through mundane means.
This is the back and forth for the last 40 pages.
Fighter = class abilities make it good at one form of winning combat
Wizard = class abilities make it potentially good at winning combat in several ways AND/OR potentially good at other stuff as well
Based on playstyle, preferences, house rules, etc. some people think the Wizard has to give up a lot to be good at combat and other stuff and some peope think it's not so hard at higher levels given spell slots and the ability to choose your 2 new spells per level. Some people acknowledge there is a gap and don't care. Some people think attacking to lower HP is a good enough niche for the Fighter. Some think since everyone is pretty good at combat, you have to either make the Fighter so much better at winning combat or give it something else.
These camps will never agree or be persuaded to see it otherwise.
Just add the mythic martial and I'll gladly keep in the existing martials for those that don't see any issues and like things how they are.
Might as well combine the mythic martial with the complex fighter as well.
So levels 1-8 = complex martial with stances, manuevers, and what not. Add some meaningful social and exploration pillar stuff
9+ = you get a power source of some sort like blood of the gods or whatever and you add non spell casting mythic martial stuff that gives more available effects and narrative control across all three pillars. Keep it martial flavored. Maybe include a power source choice that is external like guarunteed magic items/developing signature item for those that want an "everyman" as core concept.
Use the Wizard and Druid as the yardstick not the current Fighter. Find someone design minded with zero exposure to rpgs -- give them the base rules and the Wizard and Druid as example classes. Tell them to design a martial that is no more powerful or versatile than these 2 classes and let them go wild.
Make it an optional Class if you want.
Everybody is happy!