I think KBin and Lemmy could've both used being a bit more fully developed before Spez started throwing his tantrums tbh. Like, I've no intention of going back to Reddit, I very much see KBin/Lemmy as works in progress that will only get better, but I do think friendly criticism is really important and should be taken on board.
With this in mind my biggest gripe is that the magazines/communities I subscribe to are buried in my profile. Every time I'm on here I keep clicking on Magazines or searching for communities when trying to find what I'm subscribed to, rather than remembering to check my profile.
I also agree on the migration point. It's something that's a wider Fediverse problem too - Masto really needs migration that moves toots and likes as well.