I left Kitsu when they decided to kill reviews and apart from groups (that were also a mess), I don't miss anything.
I can't say I miss the site specifically, it was and still is a dumpster fire. There were so many points that just lessened the user experience. Removal of forums in favor of a twitter-esque news feed, the multiple redesigns that instead of streamlining the experience instead served to confuse the user and make it harder for them to do basic tasks like set a show to rewatch, the merger of Kitsu and Aozora leading to a massive influx of new users that didn't understand how Kitsu worked that lead to mass alienation of older users, it was just a complete mess.
But as I said in the OP, I miss the community. Maybe I'm old and just not looking/refusing to look in the right places, but I've never found a site that had a community like Hummingbird/Early Kitsu did. Even AniList just kinda feels dead. The most I see from the forum is a billion forum games and the occasional news thread.
Oh well.
Aozora
Whats that?
It was a phone app that Kitsu acquired a while ago. I think it was a tracker, but it might have also had links to illegal streaming sites for basically every show since once the acquisition happened all the new users kept asking "how do I watch this show? where's the link to watch it" and stuff like that. As I said, all the new users alienated the old ones.
The biggest issue was that because Josh (the owner of kitsu) wanted Kitsu to be a social media site for anime fans that functioned like Twitter, we had no choice but to start using global feed to communicate with large groups, but then once the merge happened, we couldn't do that on global any more because it was filled with people asking for links to watch shows (which was against the site rules)