Lemmy doesn't federated with mastodon type servers.
Kbin is the one you need if you want both reddit style fediverse and Twitter style fediverse. Lemmy only does link aggregation/reddit.
Lemmy should get kbin content but I'm not sure it federates it because kbin allows NSFW and lemmy... Does not for the most part.
Are you comparing kbin to all of the lemmy fediverse?
Because kbin is part of the fediverse and has as far as I understand been bigger then the biggest lemmy instances for a while by a good margin?