If they hadn't rushed ahead and done EW so soon, I think this would be very easy to write around. As far as I've heard, they were going to do an expansion between SHB/EW focused on Garlemald. Which would have been cool, cos then Anima could have been the final boss of the expansion instead of a dungeon boss (and the reveal as to what Anima 'is' would be a great pre-final fight reveal cutscene). Then, EW would have been level 100 and simultaneously ended the Hydaelyn/Zodiark arc of the story.
If it were up to me, I'd have done that 'in between SHB/EW' expansion, so that Garlemald and the surrounding regions got to have the worldbuilding that they deserved. I'd then have had all of the reveals, media tour, Job Action Trailer etc. for Endwalker, all say that 'at the end of the story of the expansion, you'll be level 99. Some older FF games, the level cap was 99, some it was 100. We decided on 99, because we're big fans of FF5 and in that game, the cap was 99'. But, for the final fight, due to the power of Dynamis, you'd reach level 100 and gain access to the level 100 action (as a Duty Action), a completely new move that was never revealed, and nobody outside of the dev team even knew was in the game. Warriors learning they've got Primal Rend, Samurai learning they have Ogi Namikiri, etc, and being able to throw them out every, say, 20s because it's a Duty Action. And each time one of the Scions chimes in with their motivational 'power of the indomitable human spirit' speech, rather than a mere damage up buff, I'd have it give you more and more levels. Level 105, 100, 110, 120, 150, and the player's damage numbers getting higher and higher, until we're hitting truly absurd numbers. Fell Cleaves and Midare's hitting for literal millions. And after the credits roll and you get to play the post-story part of the game, you'd return to level 99 (to avoid spoiling other players on the twist), but retain the level 100 skill as part of your kit, albeit in its current, more 'limited' form. The power of Dynamis let you spam it in the final fight, but in regular combat, that'd take too much of a toll
Which is to say, after the events of Endwalker, they'd be able to say 'ah yes due to the exposure to the pure Dynamis in the last battle, the Aether of the Soul Crystal has warped, and certain limits can be broken, which in gameplay terms means that you can choose to 'break the limits' on some of your actions and empower them with shorter cooldowns, stronger power, or even completely new bonus effects'. Now we've got Dawntrail, so I guess maybe they could use 'Solution9/Alexandria's research into souls' as the narrative device in place of 'Dynamis'
This is pretty much 1:1 how I'd solve BLU's dilemma of people wanting to main it as a 'real job', while also preserving what makes BLU, BLU (the learning). Have a baseline kit of actions, and then make the learnable spells be alternative VFX that you can use, with their bonus effects being activated within Carnivale, or while Unsync. I went through the whole list of learnable actions for the Job ages ago, to try and categorize them into one of 24 categories, and found that like half of the spells fit into one of just FIVE categories: ST attack, circle around enemy attack, circle around player attack, cone AOE attack, line AOE attack. Being able to choose not only our Glamour, but our VFX theme to match it (eg a Fire themed BLU that uses lots of oranges/reds in their Glam, or a Tech BLU that uses Drill Cannons, Kaltstrahl, Perpetual Ray etc, with the new S9/Vanguard style gear), would provide players even more options for creativity