* The FediVerse is lots of WWW sites. Some are WWW-hosting companies showing off, with all of the acoutrements of high-end WWW sites, including CloudFlare protection and lots of tweaking of the back end stuff. Others are one-person sites where someone has just set up the vanilla Mastodon/Pleroma/Pixelfed/Friendica/whatever software on a cheap hosted VM somewhere. There are lots of in-betweens. I have an account on two sites, at each of the aforementioned extremes, one with well over 20,000 users and the other with around 40.
* It's really easy to deny service to the one-person sites, and many of the low-end ones.
* Chaos.Social's about page explains that it's a couple of people running a WWW site in their spare time on spare hardware. That's a little misleading, as they've upgraded the hardware a bit. But it's still 2 people, with ~5800 users. For more, start at https://meta.chaos.social/resources .
* There's nothing global in the FediVerse. Nothing gets sent everywhere. Some commenters here can see the post cached by their local WWW sites where they have accounts. But I'm in the opposite situation: None of the places where I have accounts have cached that post, and since the Chaos.Social sysop put the 429 error in place to combat the server overloading, they actually cannot pull that post with just its URL entered directly, although simple tricks like searching for @jonty@Chaos.Social instead and reading the user timeline work just fine.
* There's nothing global in the FediVerse. Using the aforementioned trick, I see a different view of the thread from Mastodon.Scot to what I see from Toot.Wales, and both of those are different to what's seen from other places.
I've read somewhere that federation is done via regular HTTP requests which ends up really hogging down servers if someone has a lot of followers.