The number of queer users on Mastodon/Imzy is a pretty strong indictment of mainstream social networks—as if the issues with those services weren't public enough already.
I don't judge social networks in terms of Twitter-killers, just as I don't see every new Linux distro as a Mac/Windows-killer. If the goal is to provide a valuable alternative that makes a difference to people, success is not an all-or-nothing matter. This is the culmination of every innovation—when it starts sprouting niches.