The evidence is that there are lots of people who despise Musk and what he has done to Twitter who still use it. That's what speaks to it's dominance and speaks to the network effects it has.
To be clear dominance is where one player owns market majority. That is not Twitter. There is lots of evidence on this. Twitter might dominate Truth Social but it still lags far behind Facebook, TikTok, and probably Instagram.
Vendor lock-in is where the cost to switch to an alternative is supremely expensive, such as rebuilding infrastructure from the ground up. That is radically different than the stupidity of not knowing what your options are.