Lemmy has some bonus points which at the time when I signed up (I joined Beehaw around the same time) that Lemmy does (or didn't) have.

Blocking domains, blocking instances (coming soon), better UI (subjectively), user styles to add extra features, each community has a "normal topics in a forum" and a "Twitter-lite" area for different post types, I believe kbin has better integration/federation with Mastodon (which I also use) compared to lemmy, along with others I'm probably forgetting. (Edit: Forgot one lol, on kbin we can see upvotes and downvotes, as well as (on a topic by topic basis) you can see who upvoted and downvoted things, which I get some people wont like, and some will like, but we also have that on kbin, and can see those stats across instances of kbin & lemmy).

I don't follow your end of the development so Lemmy may have some of those in the pipeline, or may already have some added, but at least a month ago it was a bonus on this end. The lack of an API right now does suck since it limits the app thing, but they will have an API, several of the apps devs have already said kbin will be included when time comes, and kbin mobile is honestly real good regardless so it works out.