It is worth noting that it is basically impossible to compare any of the recent FF games to each other.
It’s standard evolution of mechanics and ideas up until IX, where it does a backtrack in mechanics, and then every game after just sort of does its own wild thing.
X has no turn party member switching, XII is a political drama with a real time MMO-like battle system based more on the very strange and different FF Tactics subseries, XIII simply removes exploration and plays around more with concepts of auto-play, both XIII sequels are radically different in play style and even subject matter (with Lightning Returns managing to stand on its own with little issue), and then XV goes in the opposite direction and has a strange road trip premise with Kingdom Hearts style combat.
As for character designs, well…yeah. You can mostly blame it on Nomura, who has a type of character he likes and does it far too much. It never worked for me in 3D outside Lightning Returns, oddly.