Dark Souls has more in common with Castlevania than with anything “RPG”.
As for Diablo type games, I personally call them “looter RPGs” as a retroactive term. Because the “looter shooter” genre that popped up about a decade after diablo is literally just Diablo but FPS.
Genre names are wack anyway. The “[other game]-like” moniker will always be more descriptive and clear, plus being a reminder that every new thing in video games is a refreshed take on some pre existing thing.