In that sense you could argue that all of astrophysics is built off of a biased sample from which we can draw no conclusions. And you may well be right, I'd think, though it is unfalsifiable.

I don’t think it’s necessarily unfalsifiable to some degree. But there’s certainly parts of our astrophysics model that are already unfalsifiable and there’s no way around that. For example, the existence of the unobservable universe by definition is unfalsifiable. We kind of just assume the locality principle and that stars leaving our ability to observe them is expansion and not them hitting the edge of the universe and getting destroyed :).

> If there’s a persistent bias in the galaxies that are in our data set or there’s a bias in the person of the local portion of the universe we can observe, then the sample isn’t random.

The Copernican principle is the default, unless we have some reason to doubt it in a particular case.