I mean to be fair, FF didn't really radicalize its battle system until VI, and even then the changes were honed into Limit breaks later and the meat and potatoes of the system is still FFV's. I mean even looking at games like XII and XIII which feel fairly alien to III and IV, you can still see their bones in the systems, just tweaked. I mean even FFX's battle system, which was taken from Tactics, is basically just the NES era FFs battle system just now with the ability to see turn order. It's hardly radical. Same with X-2's system which is IV's system just with characters able to act simultaneously so it feels faster. The biggest leap is really III to IV with the advent of ATB which added a level of challenge and urgency to combat that most turn based games couldn't match.

FFs bigger change has always been development systems, which have almost never stayed the same. But honestly, with the possible exception of the job class system from V, which itself is only sort of newish within the genre, FF has never really had a development system I felt was so good it needed to stay and just be refined.