Also, I've seen other game series evolving their formulas over time. Final Fantasy did it, Dragon Quest did it, Fire Emblem did it, Legend of Zelda did it.
Take Final Fantasy VI (1994) and Final Fantasy XIII (2009). Quite a difference, in both how they look and how they play, generally and in what concerns combat systems. For better or worse.
Combat of classic FF is not all that different between games. Your complaint regarding enemy design/samey spells etc also applies to FF. What is indeed different is the underlying character development system and whether characters are unique or act as a job container. Some of those changes are mixed bag execution wise but yeah they do keep things fresh I guess? The big radical departure which is not "contrained by old console anymore" XIII onwards, I would argue is shit. So newer isn't better. XII is also a radical departure and plays like a major single-player MMO (and this is bad)
It is not that ATLUS doesn't try to do anything at all. Devil Summoner series is basically ATLUS attempt to change the combat into kinda RtwP which is a mixed bag execution wise. With P5 Scramble I guess we also got some sort of beat em up action games.
Personally I wouldn't mind them changing the formula a bit especially on the character development system. But as I pointed out, I don't really play these games for muh combat so there is that.