They're riding on the network effect that they won with zero-friction user adoption, startup capital and a client that was okay at the beginning. Now the client is pretty darn good, they're basically AOL Instant Messenger now, except people actually want to pay.

As an aside: Hopefully their security team is phenominal, they are gonna need it. Personally, I'm extremely distrustful of Discord's future CIA (infosec term) of their service.

Why do I think Matrix isn't going to win after a client polish round or twelve? Well, its a little bit weird to say iPhone users who will have to wrap their head around one or two concepts about bridging and so forth, as opposed to Discord who has an API and a business unit dedicated to interoperating it with other services. Why would Facebook link to Matrix bridges when theres no money at all?

Why has slack not achieved this? the onboarding flow wasn't/isn't as easy and it is definitely targeted to business or institutional use would be my guess. Casual users like blinking tiny gifs of :kappa: and the gamers are already there.