You're right but Arkham Asylum was the only game that innovated actions games with that combat system (aka killed off the whole high budget hardcore action game genre), The first few Assassins Creed, Spider-Man, etc all took elements from that game with stealth and combat.
Arkham City was just that game 2.0 with a bigger map. Knight was the same thing again but with a tank as a batmobile. But yeah, they haven't done much to add or refine the gameplay like you said.
I know its all the same thing, but I took that as Arkham borrowing more from Bioshock's recent success than trying to intentionally be a metroidvania. We saw Dead Space and other games do the same thing in that era.
And yeah, Knight still looks crazy. I hope the rumors from the Nvidia leak for RTX remasters of Arkham Knight (and Bioshock games) are true.