Apart from what has already been said (politics, basic UI) there are a couple more things worth mentioning:

• Kbin’s interface is muuuch more customizable than lemmy’s: browsing form a web browser (desktop or mobile) let’s you modify your viewing experience as much as any mobile app for lemmy (but lemmly itself doesn’t). From infinite scrolling vs pages to font sizes and such.
• kbin allows for (mastodon-like) boosting of posts, which is like a super-upvote that lemmy just doesn’t have.
• on kbin you can subscribe to mastodon users aka federate with mastodon. Something that lemmy also can’t.

Other than that only personal taste matters in the end, and both federate with eachother, so enjoy it from wherever you are.

I was confused what boosting is. Docs said it’s basically a repost/share.

So I think super like is misleading. Even if your super liking is the reason you share it, they’re two different things.

So I think super like is misleading

It's literally not. Over here, on top of the "repost to your profile under your boosts section" functionality it's intended to have, it also counts as 2x rep for the poster.

Key word also

The presence or absence of that single word doesn't change the fact that nothing OP said was wrong eh ;P

Nobody claimed what they said was wrong. The thesis is that it may be misleading (through omission of the second half of what it does).

See, the problem here is that you're treating an off-the-cuff casual explanation as a "thesis." Please don't bring this absurd habit over here, where people have to feel compelled to cover absolutely every interpretation and hedge every outlier for great of getting nitpicked to hell and back. Literally no one enjoyed that environment.