Well, yes. The entire Witcher trilogy and Gothic are action RPGs, since they are games with "RPG framing" (branching dialogues, storylines affected by choices and consequences, etc) and an action, mostly-skill-based combat. Diablo is a hack'n slash, as you said, since its gameplay loop is entirely focused of whacking hordes of enemies and there's hardly more than that.
The point is that you'd have a hard time trying to convince a general audience that they aren't all under the same "RPG" label. The nuance is not particularly valued outside of certain circles.
Try to convince someone that JRPGs are not RPGs at all. "But it has RPG in the name" they say.
