I’m running an atproto app and it’s perfectly capable of ingesting the entire firehouse as it comes in. It costs me maybe $10/mo and mostly because I haven’t fixed some memory leaks.

Of course, few of records that come through are relevant to my app so I don’t store them.

If I wanted to store gigabytes of records (like Bluesky) for millions of users forever then yes it would be more expensive. Which would be the case with any tech! What are you comparing it to? How is this a downside of atproto?

Mastodon instances aren’t a valid comparison point because by definition they’re small-world. They don’t serve millions of users.

If your point is that you want small-world atproto, that’s absolutely possible. Take the Bluesky server codebase and make it so that it ignores incoming content beyond some criteria (like “follows of server member list”). You can recreate Mastodon experience on atproto, it just hasn’t been very interesting to anyone so far AFAIK.