I am sorry I couldn't aptly understand you.

did people migrate from twitter / reddit to discord / slack? That's an interesting phenomena if it has happened that I wasn't aware of, do you have sources I can read up on it more?

anyways, my point was that "usability in general" is not the key (reddit has famously terrible interfaces, for example). it is being really usable on the core functionality it should provide (like having tons of content to discover, and getting your content to tons of other people, in case of social media) is what matters.