The problem with Dissidia is the leveling is extremely hampered by load times and the lengths of battles. Unlike most Final Fantasy games where you're in an out of a battle in a matter of seconds, passively killing hordes of monsters, you're fighting only one opponent at a time and often enough, they don't yield enough XP, AP, or what have you. It just takes too much time.
Fighters can still change a lot over time though. Perhaps they'll take Dissidia 3 to console(s) and alter the gameplay enough to appeal to more casual gamers like myself. I don't have endless hours to devote to leveling up a ton of characters, most of which I don't even enjoy playing as. I've never gotten a character to level 40, and the game is really supposed to open up once you reach level 100. That's absurd.