Indeed - the UX here is absolutely fantastic.
My only concern is so far I haven't seen quite the same level of activity that I've seen on Lemmy, but I'm optimistic this could change, especially if some existing subreddits decide to start pointing users here...
Indeed - I think people seem to have this ill-conceived notion that Twitter has to fail for Mastodon to succeed.
From my perspective, both are doing just fine. Mastodon has developed a community with, in my opinion, much higher quality discussion, and well, Twitter can keep being twitter.
That said, what I do think helps here is that Kbin has a much lower barrier to entry. I find it much easier to sign up on here than trying to determine which Mastodon instance to use and I think that helps tremendously.