That’s a very pessimistic view.
Yes, if you want massive servers with millions of users, like Twitter, then it is going to be run by a large corporation, like Twitter.
But that doesn’t mean the smaller sites will have to go away. Just like the fact that there are plenty of smaller news/commentary/discussion web sites (including this one), despite the fact that there are also much bigger sites, that have higher operating costs and are run by bigger businesses.
But even if we don’t find a lot of smaller servers in the future, it doesn’t mean everybody is going to be subject to the whims of the big players. The very fact of how federation works means that one player can’t impose its will on others. If we end up with a few big players that develop objectional policies, then those sites that disagree may choose to not share with them (or the big players may choose to cut off the connections).
So instead of making it impossible for these unpopular groups to have a voice, they will be forked off into an independent ecosystem. Much like what’s going on today, but without the need to deploy a whole new network of servers running new software.
But it’s unlikely to get to that point. Again, I ask that you look at what has come before.
There are many big players in the e-mail space, but there’s nothing stopping you from running your own mail server. Yes, you may need to jump through a few technical hoops in order to get mail from your server to be delivered universally, but these are based on policies that most people support - like blocking spam. Although there are not many mail servers run by individuals, there are hundreds of servers run by every service provider and hosting company on the planet.
The platform doesn’t turn into a business, because there’s a very clear difference between the platform and the servers that implement it.
As for government control, nearly every human being on earth, if given sufficient power, will want to abuse it. Whether they choose to attack Internet services or newspapers or broadcast TV is almost beside the point.
But with a federated communication technoliogy, no government can take it all down. Even if the big players are all ordered to clamp down on content, there will be plenty of servers running in other jurisdictions that will not play along. And unless the government decides they want to censor all traffic everywhere (as China does), there’s not going to be much they can do about it.