Fyi in case anyone reading this didn't know, Element is a client for the Matrix protocol, by the people who are the prominent developers and supporters for the Matrix Foundation.
Matrix only has inbuilt support for 1 on 1 calls right now, it (Element) uses Jitsi for group/channel calls. Native Matrix group calls and video calls are coming very soon, along with (hopefully) push to talk in the Element client, and custom emoji for those who like that stuff.
With respect to the Element devs (I want to see it succeed) it's UX and polish is night and day compared to Slack. I struggle with Element and I've been using messaging apps my whole life.
Element doesn't have inline video embedding for any link, the emoticon support sucks, and the voice chat leaves a lot to be desired.
I like Matrix and I like Element, but let's not pretend something missing features that forums have had since 2007 is going to have a user overlap with Discord. It's much more cumbersome to use in comparison, and much more work to set up.
But you don't have push to talk, which is the killer feature for gamers. Proper push to talk will capture key presses even when the app doesn't have focus, the key difference with most other implementations.
And having that feature exposed to the web is a security nightmare. Unless you have a native app for your service, it's unlikely to ever have that functionality.
You can freely choose a real server and can talk to anyone on any other server.
[0]: https://element.io