I complete understand your qualms about Mastodon. Even as an avid user of it, I still know of quite a few instances and various admins that are closed off and ban happy. If you piss the wrong dude off in certain places, off you go. That and since these servers are maintained by either one dude or a small team, it can be worrying to how they handle your data. But then again, that data trade off is something applying to any social media, be it Mastodon or Twitter.
Blue Sky…honestly, I don’t know what to say of that project. The internet has changed a lot since Twitter was founded and a lot of promising social medias and platforms have gone up and died off because no one is willing to fully jump off the big boys. That and making MONEY off these platforms is one of the biggest hurdles too. Vid.me, Vine, countless freaking Twitter clones, they all failed cause they couldn’t attract enough people or sponsors to even keep the lights on. The biggest reason Mastodon isn’t on this pile is precisely because keeping decentralized means the costs of upkeep goes to the admin AND also because instances could cater to certain niches instead of the shotgun approach of trying to attract everyone to the platform.