The terminology describing these differences is really bad. ATB is still turn-based in my opinion. Namely, you still are taking turns to perform actions. The ordering of the turns is just determined slightly differently.
The main difference with FF10 for example was simply that when it's your turn, it pauses time so you don't have to rush. Well people seem to ignore the fact that in FF9, time continues while you're deciding which action out of the main list but pauses if you go into the magic or item menus. So if you really need time to consider a strategy, that's an easy workarond. The main distinction for me is whether you can control your character's movement in real time or not. And whether that movement affects the way battles play out.