Zelda II even had experience points, and Wikipedia counts all the other games I named as ARPGs. There is no way in which Diablo was the first ARPG.
Edit: Maybe the influence of Diablo is more that it effectively ended the era of Western/PC turn-based RPGs. For Japanese RPGs, turn-based (non-action) RPGs did hang on for longer, e.g. in form of Final Fantasy.
Fact of the matter is that ARPG today generally means a Diablo-like game. It defined the genre that we know today as ARPGs. You can name other games ARPGs if you want, but it has nothing to do with Diablo or the genre that Diablo defined.
I'm not sure why this sort of thing is so difficult to understand.
Pretty much all modern Open World RPGs have real time combat and are therefore called action RPGs, e.g. by Wikipedia. But a game like Elden Ring doesn't seem to me particularly Diablo-like.
Edit: Maybe the influence of Diablo is more that it effectively ended the era of Western/PC turn-based RPGs. For Japanese RPGs, turn-based (non-action) RPGs did hang on for longer, e.g. in form of Final Fantasy.