That makes total sense, backfilling everything an account has ever posted, even if it's thousands of posts, would be a bad idea especially for smaller instances.
But if it was just backfilling a small number of posts would that be ok?
Like, backfilling 5-10 posts when you follow someone?
Or if there was an option for the instance owner to set how much backfilling there is, so they could adjust it according to their available resources?