D3 is vastly different and superior to D2s gameplay design, D2 just copied and slightly improved from D1 so the design is not even from D2, it didnt create a mold for anything as there were a few aRPGs before the first diablo even released so its just a copy of a copy.
D2 is a decent game but its far from being a pinnacle of anything, its gameplay alone is just acceptable.
Only the cultist fans would claim D2 was the pinnacle of anything, the truth is the game is just average as a game and its gameplay systems were just copied and modified from previous aRPGs.
The best aRPG is the one with the most active playerbase which is probably lost ark currently.
Simple fact is D3, PoE, Lost Ark, Grim Dawn and other aRPGs are far superior in actual gameplay, so claiming D2 is the pinnacle of anything is just lying to yourself.