Come play Dungeon Fantasy RPG!That's because anyone who wanted a cool martial left to play another game, so the martial players that are left either simply don't care about the game aspect or have some weird impotence fantasy where they want to play a town guard +1 alongside Dr. Strange. The people who like the current fighter just don't care much about effectiveness or driving the plot through character abilities.
Mundane flavor isn't inherently in tension with high effectiveness. I abandoned 5E for Dungeon Fantasy RPG (Powered By GURPS!) a while ago, and one of the awesome things about it is that warriors and wizards are both extremely attractive and fun to play. ("Knights are OP! Wizards are also OP! It is awesome!") And they synergize well together too.That seems part of the conflict between Fighter fans.
Fans who like the "mundane" Fighter, prioritize mundane flavor, and dont care about effectiveness or class balance.
So fans who do care about effectiveness are left less effective − in the sense of being shut down by certain narrative scenarios that happen at high tiers.
At the same time, it is probably the mundane Fighter fans who start to ... end the game ... after reaching level 8 in the mid tier. So these Fighter fans rarely see the tiers when magic narratively changes the game.
But DFRPG wizards have a different feel than 5E wizards, and DFRPG warriors have a different tactical menu. Instead of Fireball or Evard's Black Tentacles to take out whole roomfulls of mooks at a time, round after round after round, a DFRPG wizard might be able to glue a 10 yard diameter of mooks to the floor but then he's tapped out until he gets at least a few minutes' rest (DFRPG combats are usually over in a few seconds), so it's up to the warrior to walk over to the trapped enemies, approach them from behind, and stab them in the kidneys for triple damage without them getting a chance to parry/block/dodge. Since the opportunity to defend is DFRPG's equivalent of 5E's ever-increasing HP totals, it's sort of the equivalent of replacing 5E's Fireball with a save-or-lose spell that both immobilizes and multiplies incoming damage by x10. As you can imagine, warriors are much better at exploiting that kind of spell than wizards are. And again, the fact that wizards can cast spells in every fight but can't really cast multiple big spells in any given fight is also a big factor in making fighters fun; ditto the fact that wizards (and bards, druids, and clerics) have some amazing buff spells they can cast on their buddies in advance, which again work better on mighty warriors than they do on casters (or hirelings, or summoned monsters or illusions).
If anyone out there is interested in experiencing DFRPG combat or class balance ("profession" balance), I'd be happy to run you through some practice fights. It's so much fun.