Thinking a new social network platform is destined to fail because it's a copy of something, but without the impetus that produced the original.It's the "make something people want," but more "make something they use for X."
You need the original purpose. It has to be to make something that isn't itself. Myspace was mainly novelty and music, Facebook was for status minting from ivy colleges, other ones are for an exogenous purpose as well. Politics isn't a useful unifying principle. I helped run a progressive political precursor to one of the major ones about 20+ years ago, and it only existed because it was tolerated by part of the establishment, and it could not survive a truly hostile environment.
Gamers made discord a thing because it was for playing games. Hipchat was about making code, and Slack was a way to manage people. Reddit was for sharing alternative/emerging culture.
A divergent platform needs a basis in the culture, and the current generation of censors came up in divergent/alternative culture, so they have a more sophisticated idea of what nascent opposition looks like than the old ones.
Short version is, we don't need a decentralized social network, we need new culture that produces networks, and courage to create that culture.