The difference with a federated system is that you can leave kbin without leaving the entire ecosystem. Don't like how kbin is being run? Well, you can go join Fedia, or some Lemmy instance, and go right on following the communities you enjoyed, without losing anything terribly meaningful (at worst, your post history, and Reputation if you value that).
Imagine if Reddit had been part of the Fediverse. You could abandon Reddit, but keep all the things you liked about it. That's the biggest advantage of decentralizing access to content: while Reddit has a monopoly on being Reddit, kbin or any other Fediverse instance does not.
EDIT: Yeah, yeah, editing after being downvoted. In case it's unclear, I'm not telling this user "If you don't like it, leave." I'm saying the nature of the fediverse is that leaving one instance does not necessarily mean leaving the fediverse. If what they suggest comes true and kbin.social eventually does something to provoke a mass exodus as Digg and Reddit have done previously, people can basically just move next door and go about their day as normal instead of being uprooted from all of their communities.