I'm here to add my opinion that FF9 is superior to FF7.

In general, I prefer when your characters have set classes. It feels like it lets the characters have more fleshed-out personalities.

Without spoiling anything, it allows you to tell story through the medium. Have a character who spent his whole life in one class, relying on specific skills, and he maybe goes through a huge fight to signify that he's changed for the better? Congrats. You have a class change! Now you're a level nothing!

Maybe someone traumatizes a caster, and now they can't concentrate, giving them a chance to fail their spells!