I haven't really used lemmy but it didn't appeal to me. kbin feels more familiar to me (as it's very similar to how reddit works). kbin is super cozy, so I'd recommend it.
since you're on lemmy.world you should see all lemmy.world stuff easily. here on kbin we've been having some federation issues in the past and i'm not sure everything is 100% synced yet but I've definitely run into missing posts here and there.
Ironically, kbin's federation problems seem to surround other kbin instances lol. I think fedia.io broke their federation. There's not really a lot of kbin instances tbh. It's mostly just here on kbin.social.