I'm personally fine with Zod being at level 83, if he was the final boss it'd have been super predictable and that's no good. But, one way I could see it have going quite well is if the push to Garlemald and retaking the capital was fleshed out to a full expansion, and Anima was the final boss of that, with the shocking pre-fight cutscene (equivalent to Zenos fusing with Shinryu in SB, or the whole Emet/Ardbert bit in SHB) being the revelation that Anima is the emperor's corpse reanimated by primal-ing, would land pretty well I think. Would also allow for Ilsabard to be a bit more fleshed out in terms of geography, maybe we do a SB style pincer attack and have Gyr Abania side push on one front, and Nagxia/Dalmascan zones (sp?) on the other
Then I'd make it so that for EW (now being 90+), same bosses. But if I was in charge of everything it'd be said, at any media stuff/fanfests/everywhere gaming journalism has ears, that 'when you have finished the story, you will be level 99, as homage to some of the older games'. If asked about 'why not 100 like other older games', I'd just say 'it was a tough decision because yes some are 99 and some are 100, but in the end we went with 99'. However, during the final fight when the 'big hero moment' kicks in, you temporarily break limits (something something dynamis) and become level 100. You gain access to the 'level 100 skill' as a Duty Action (20s CD, no other restrictions like gauge costs), having never been shown anywhere before, so everyone's losing their minds mid fight because they just got to see Double Down or Primal Rend for the first time. The boss's reaction of 'how are you getting stronger' and frantically flailing in desperation is wholly justified, as you've apparently just mastered a completely new move seemingly instantly, with zero practice beforehand. After the fight, you keep the new level 100 move, but are returned to level 99 so as to preserve the surprise, and it has the new restrictions like Gauge cost or longer CD (blame it on 'there is less dynamis to work with back on home planet' or something).
Lastly, in the final duel with clingy ex BF, instead of having 6 stacks of 'extra lives', you have infinite, it's a victory lap of sorts. Your goal would be to drop Zenos a certain number of times, as currently. After he drops the first time, he does his reaper fusion thing still, after that though, is different. Instead of instantly 'killing' you every time you 'kill' him (very stale imo), he doesn't do that. Instead, each time he or you drop to zero HP, you immediately restore to full HP with that glow around you (cos dynamis), without losing control of your character (no down for the count rubbish), and your level increases. At first, by small increments, 105, 110, 120, but then 150, 200, 300, 500, and finally if you somehow die that many times, 999. With this, your damage numbers and HP values also increase to insane amounts, and as Zenos gets beaten over and over, his 'level' increases too, with his HP bar getting larger and larger, his attacks doing more and more damage, with the scaling being such that each consecutive phase is shorter than the last (the level ups get faster and faster), eventually the two of you reaching the point where you're doing literal millions of damage per GCD against each other, because there's no other point in the game that it'd make narrative sense to have numbers like that, and it'd be cool to have just one time. Tell me WAR mains wouldn't enjoy seeing their Fell Cleave crit for 3.2 million damage
Maybe kinda cringe, but hey we're playing FFXIV, that's a bit cringe by default