I think his point is that a system that allows anyone to be anything makes them all essentially the same character. To quote The Incredibles, "when everyone is special, no one will be." This is a major complaint I have with Final Fantasies 6, 7, 8, & 12: the characters are so functionally the same in the progression system that they feel incredibly generic in battle. It isn't like in Final Fantasies 4 or 9 where the characters have set roles and, thus, have unique identities in battle.
My favorite Final Fantasy titles are VI and IX. It's been a while, but I don't remember really playing them differently. I just equipped skills then leveled up. Based on what you're saying, I have no idea how I completed IX. I'm assuming I just stumbled through the game then leveled up high enough to beat the final boss.
I plan on buying Bravely Default, mostly for my brother though I also want to play it. We'll see if I ever get around to it. In the event that I do, I will probably just brute force my way through the game instead of paying attention to classes like I'm supposed to.