Yes, you can run a PDS, but while it might be true that you can self-host a relay with a couple thousand people (I didn't find anything about this in that blog post but I don't see why you couldn't), using a limited relay like that would mean this would not be a full/real instance of Bluesky (unless you disconnect from the rest of the network, but then why even bother)

So let's examine the problems with relays here:

After recent growth, our out-of-box relay implementation (bigsky) requires on the order of 16 TBytes of fast NVMe disk, and that will grow proportional to content in the network.

Core Bluesky engineer's blogpost

In July this was "only" about 1TB, in mid November around 5TB, and now 16TB? That's insane growth if you want to self-host that, and will get expensive really fast really quickly, especially since fast storage is important here. I don't think many individuals have the resources to self host this just for themselves.

Another critical problem is that when more people self-host relays this has the wonderful side-effect of increasing the necessary computation power and network use, because Bluesky scales O(n^2 ) , which is really bad if you want anything close to a decentralized network.

So yes, it is true that it scales down terribly, this is by design. It's a step up from Twitter, because this time multiple corporations can control it instead of one, but it isn't that good either.