I think that app does not make it successfull. App can be awful, because friends that use it with us are the real value of social media. So if you’ll convince most of your friends to use Mastodon, it may be pretty good social media app. You are right that non-technical people may find hard to use these ‘super secure alternatives’, but apparently media buzz about evil Facebook did the job and nowadays it’s not always obvious that someone is on Facebook. I have some friends that decided to use apps that are not really social media apps as substitute to Facebook - and it turns out that reddit or signal may be a great social media place even though it’s not really designed to be one. :-)