I would argue that for most purposes, kbin IS lemmy. It has 1/10th the native user-count and 1/100th the native comment count according to https://the-federation.info/platform/73 and https://the-federation.info/platform/184. I get the sense that a large part of what people use kbin for is as an alternative UI to access lemmy communities. It seems much further from achieving a critical mass of native communities though.

That's not a knock on kbin, people use it an enjoy it. But I'd contend that to the extent that either kbin or lemmy are "reddit replacements" at all, they act together as a single federated option with multiple UX's rather than two discrete options.