I think most Final Fantasy fans would still consider the ATB systems to be turn based, just depends on how pedantic you wanna be. You're still taking turns, you're just not necessarily taking them in the exact same order every time.

Also if you're gonna be that pedantic, X is not a turn based system either. It's a conditional turn based system where characters with a higher agility stat take more turns. Almost exactly the same as ATB just without the need to input your actions as fast as possible. (If you have ATB on active instead of wait mode.)