Sorry for the late reply, but if all we care about are users we already know and if we are all willing to run our own relays then there is no difference in censorship resistance between Nostr and Mastadon. Heck, if you aren't worried about wide availability then you don't need even need it to be a microblogging platform; just use something like Wordpress and make an ordinary blog. The advantage of Nostr is that the ability to discover and interact with a new user is not up to a third party administrator. It's up to the users themselves being lucky enough to win the relay roulette, choosing a relay that aligns with their values and interests and displays the other's notes. This still is not even close to ideal, but it is currently far better than any other platform when it comes to connecting users and being able to find posts about things you are interested in.