Retrospective averages are used by guys like Nate to memory hole the fact that all the big name polls had Biden ahead by 10 points.
It is only the big name polls that are quoted by the media during the actual campaign.
In any case, even if the polls were systematically off, and they may have been, that doesn't justify calling them all propaganda, or bs. It isn't even evidence of it. Because, as it happens, polling people is effing hard.
Look, there clearly are some "bullshit polls", and there are partisan polls paid for by candidates which tend to be favorable to them, and there a good polls with consistent bias, a kind of "house" effect as a consequence of their sampling methodology, etc.
That's why Nate Silver does averages of polls, btw, and weights polls in the average by their accuracy in previous elections.