"Balance" and FFXI are mutually exclusive. If you look at the trends that formed in that game over the years, it's pretty damn clear.
That aside, the reason people stick around is because of tribalism (AKA the nonsense that turns everything in an "us vs them" scenario), and the attachment formed when you spend a shitton of time on something. Old school MMOs relied a LOT on that, and people expectedly cling to it to justify the many hours spent on some of the stuff from those games.
This already exists. If you like the aesthetic of Kain Highwind and jumps, you're going to play a dragoon. If you like hitting things with your fists and martial arts, you're gonna play MNK. If you like black mages and nukes, chances are you'll play BLM. If you like pet classes and utility, you'll play SMN. If you like big axes, active mitigation and rage, chances are you'll gravitate towards WAR. If you like swords you'll be lured by PLD.they do need to give each class something that will make the player look at them and be able to choose a reason WHY they want to play that class, not just trying to decide on HOW they wanna dish out the dmg.
Granted, you won't find what you like until you actually try those jobs, but that's sort of the point of playing the game. Just be glad we don't have to reroll every time we want to try a new class.