Their loss, should have not fully switched to that one to begin with.
Also, a company can enpoopify itself yes, everybody loses but the board members. 
Imagine if they kept being nice humans, everybody would win.
Meanwhile, gamers are supposed to be more tech-savvy than your average Joe so can hopefully migrate elsewhere.
Doesn’t have fancy borders/animated avatars sure. Not a big loss to me.
It is fundamentally a different platform so yeah, you won’t have feature parity yet it has the edge on other topics + is FOSS and potentially more future-proof than a company’s product.
Real time low-latency communication is one platform, chat/messaging is another entirely different.
Discord was kinda a 2 in 1, but soon to be gone entirely. 
It’s probably on the roadmap already, don’t you worry. 
For chat purposes? There is a lot available that is also self-hostable like Rocket, Mattermost etc etc…
Also, I can’t even see how Stoat looks without creating myself an account, quite bad marketing to get people to migrate to a UI that you cannot even see while Discord is all about UI/ease of use in the first place. 
For real-time low latency voice communication, Mumble is still probably the king.
We need 2 tools to replace Discord here. 