Each action requires so much ATB, the bigger things more of it. But it is just the difference of waiting a couple of turns. You'd still have to spend a turn other FFs using an item and then casting again. So there isn't much of a difference. Spells don't have cool down just the time for the ATB to fill again. And you can get equipment that speeds up the ATB meter as well haste. The time you spend wouldn't be much different.

But there is also tricks in the combat system, every other full cycle of ATB when you switch paradigms it will be refilled at no wait. So it is actually to your advantage to switch paradigms regularly to fully maximize your effectiveness in combat. It's far more quick paced and reactionary than past games and flexible to allow that reactionary stuff to be mean sometime. If a big attack is coming in you can switch to turtle and protect yourself, any other FF game you'd just have to eat the damage and pray that the game wasn't feeling especially cheap or mean that round.

I still stand by Lightning Returns and FFX-2 being the best combat systems Square Enix has made for a FF game, nothing comes close to matching the enjoyment. I actually like going into combat in those games, it's fun and active. The only other one that comes close is FFX. The rest are very simplistic affairs that too easily fall into button spam with only FFVIII providing something more active with Squall's timed attack bonus.