Diablo III and IV don't have a monopoly on the genre. There's Titan Quest, Grim Dawn, and the Borderlands games, all playable offline, even in multiplayer. They're not exactly Diablo, but you'll hardly get closer than Grim Dawn, and there's no reason you need to be married to the Diablo IP anyway. That kind of brand stickiness is how you get taken advantage of.

Personally, when something like that doesn't respect my values, I'm not even finding myself tempted by them these days. Oh, it's always online? It's dead to me. There's a deluge of other stuff to play, including games that are similar but respect my values.