Eh, I'd make the argument the fediverse is overly inefficient, way more than it has to be. (But that doesn't seem to be the actual point of the post, instead rehashing the same "distribution = good" thing without bringing anything new to the table)

Here are just a few things that could be fixed without needing to centralize fedi:

• A vast majority of instance software will store all old remote non-media data (that could easily be re-fetched when needed) permanently, even if nobody has seen it in years.
• If you're lucky enough to be on instance software that backfills replies (GoToSocial, the Iceshrimp rewrite as of a few days ago, Mastodon in an extremely limited capacity), it will be done slowly and recursively, when much better alternatives that don't need to deal with easy-to-get-wrong recursion handing are possible. (There is work going on to improve this, but it may take a while for it to land on enough instance software to make a difference)
• The obvious thing everyone harps on: Abysmal media caching defaults.
• No batching of activities. And relatedly, all sent activities are individually re-signed for each instance on each delivery (to be fair, handling this in a privacy preserving way is hard)
• No batching of fetches.
• RSA, just to make the above signature situation even worse
• Mastodon. Just in general. It's by far the most heavyweight fedi software I know of, running on a synchronous and poorly threaded tech stack that's is not very adequate to the fairly IO bound (when not using authorized fetch) and very concurrent AP use case. Running Mastodon for any instance less than ~500 active users is extremely overkill and you'd likely be suited with other, lighter, instance software if you don't need any of the features that are Mastodon exclusive (which there aren't that much of).
• Pleroma database rot, an exemplar of why the C2S advocates' model of "store the raw JSON for everything" is a terrible idea (thankfully the C2S model hasn't taken off enough to be important)