I use Discord every day and I disagree with you. I will go wherever the communities I interact with go. If Twitch starts to incentive streamers to move their communities to Twitch Desktop, it is going to be difficult for Discord to do anything about it.

Of course, there are plenty of Discord servers not associated with specific streamers or related to Twitch. Those will be harder to touch but I don't think Twitch cares about them anyway.