I'd argue that Kbin's a bit more - it's viewing and publishing capacity for users exceeds that of Mastodon or Lemmy given that it bridges the "Redditverse" and "Twitverse" styles of communication exceptionally well. Content is more discoverable as you've got the ability to follow (and block if need be) not only people, but communities and even entire domains, and the search capability scans both Mastodon and Lemmy.
For those using Kbin, your Mastodon posts and traffic show up in the Microblog section.
In my view, Kbin holds the most potential in the Fediverse, both for the average user and the content creator. It's pretty damn cool to be able to view and publish to pretty much every major instance, regardless of the platform they run.