Yeah, they all really do feel like "Oh you want to stop playing World of Warcraft, but still want an online game to play? Try Second Life!" and I think that's partly because there isn't an app out there that feels like Discord besides Discord. Cinny (Matrix), IRC, and Stoat come close, but none support voice calls at this point, at least that I can find. Matrix itself supports calling (though I think that's still experimental), but Cinny doesn't. If it ever ends up supporting voice calls, that will likely end up being the Discord alternative In wouldn't feel bad recommending.
Until then, though, we don't really have a true Discord alternative. Just various chat apps that don't quite hit the mark.