Matrix is probably the closest to Discord overall. If Element is bugging out on you, it might be worth trying other clients. Nheko worked well when I tried it, for example. Do note that the matrix.org homeserver is sometimes overloaded, so if you're having responsiveness issues, choosing or running a different homeserver will probably clear them right up.
Mumble.info is great for voice. If your text chat needs are pretty basic, it might be a good fit. I don't think it saves message history.
XMPP is a protocol, not an app. If you you saw an interface you didn't like, you could always just use a different client. I don't usually recommend it, since setting it up with all the features people usually expect is a bit complicated and error-prone, but it would probably be fine among a small group of friends if one of them has tech skills. I don't think it offers voice, at least not in any widely-supported way.