AT is not yours - it belongs to Blue Sky pbc. You can link your own domain to it, but the user interface belongs to Blue Sky and they will block you if they want.
Sure, Bluesky can block you from showing up in Bluesky the application. But if they do, you can still host your own content (as is being done here) or access it via alternative apps (like Blacksky).
This is like saying that "RSS isn't yours because Google Reader can block you."
What does “they will block you” even mean: this article is talking about hosting your data on your PDS and presenting it on your domain.
- Blacksky has their own full appview for bluesky nowadays + relays and PDS w/ something like 60-70k users. It's small compared to the total bluesky count but it's still very sizable.
- There are countless atproto relays running independent of "big bluesky" and they only cost like 20usd/month max nowadays to run.
- Likewise it's trivial to host your data on any thirdparty PDS and scaling up a PDS community isn't terribly hard (PDS scale linearly up to like 500k users and then it scales linearly past that by just periodically launching a new PDS part of your "cluster")
- And most importantly the UX on migration is getting a lot better so it's reasonably approachable for average users.
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Side note but I noticed your name. Are you "the direwolf20"?
Nowadays you can run a relay which maintains the current firehose of events + some amount of backfill (commonly a day, week, or month).
Appviews listen to the relay and can save what they care about and can look to other relays if they need more backfill.
So in practice you have your relays for regular use which handle large amounts of outbound traffic and then you have "archival relays" which store all or large portions of the history.
And in the eventual future "archival relays" will likely end up providing backfill for extremely old history via something closer to IPFS (it's the same underlying data structures so this isn't a major change, just nobody has done it yet).
And of course in the event a particular bit of history is missing, a relay can just ask the PDS for a new copy of the data.
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TLDR: The 20usd/month is for a relay with like a month or so worth of backlog attached and you can get by with less/cheaper or with more.