The main thing I would point to is that Matrix itself only does text; the Element client uses Jitsi to add in audio/video calls and screensharing [...]

Matrix VoIP is a thing, and it's usable for audio & video on many clients, element and fluffychat come to mind, but probably more.

element call is also coming into element (and possibly other clients) for video calls and screensharing

My other gripes are just with the user interface, [...] it really doesn’t look like Discord

why does that matter?