I think the Final Fantasy series has always been about evolving and trying new stuff out. They've very rarely stayed the same from game to game and almost always have tried very new things with each release.
FF2 totally changed the character advancement system to be based on combat actions.
FF3 introduced a basic job system.
FF4 had ATB combat for the first time and a rotating cast of unique characters.
FF5 used a greatly expanded job system.
FF6 did tons of new stuff, from tactical multi-party battles to the ability to switch people in and out of your party, the esper system...
FF7 was a drastic departure in tone and style, not to mention visuals, plus the materia system, limit breaks etc
FF8 took a whole new approach to advancement again, plus a totally new magic system and pushed even more into sci-fi territory.
FF9 was probably the 'safest' in that it re-used a lot of concepts from earlier games - I'll give you that one.
FF10 used a new combat system - turn-based, but with free switching within combat and character agility mattering way more, plus again totally new character advancement. FF11 was an MMO, nuff said.
etc.
While technically FF2 and 10 are both "turn based" they're extraordinarily different games in terms of how combat, progression, equipment.. EVERYTHING.. works.
SE trying new stuff with FF12, 13 (and 13-2, 13-3) is to be expected!