I don’t think it’s unreasonable to argue centralization is a naturally occurring phenomenon. It’s everywhere. The U.S. left Afghanistan and was replaced by a different centralized entity. One could argue how decentralized those “tribes” were, but regardless, after the U.S. departure they recreated a similar structure.

Complexity comes hand in hand with size. The OP is a chart of the different email providers. Can an individual run their own email server? Yes. And doesn’t it get more difficult after a certain number of users and require hiring specialists? Yes. But still, such large services exist, and a majority of users turn to them.

If the fediverse lives there will always be small servers, but we can expect to see really big ones. If we don’t want them to be corporate recreations of gmail and yahoo and hotmail I’d argue we should figure out a platform co-op/worker co-op model, including the necessary funding and specialists.