That's my gut feeling.
I don't think it's at all impossible for Biden to win, but that's my gut feeling.
To be more specific: I think the "Red Mirage" scenario will happen. Trump will have a lead on election night and he and the Republicans will pull some fuckery to stop mail-ins from being counted in the right places.
If it gets to the Supreme Court, either Biden and the Dems will pull a Gore and surrender the election without a fight, or the Court will rule in his favor and hand him victory.
History will repeat itself.
I think you might be right, maybe, for a few reasons. Some states, like florida, have to have all votes counted on election day so theirs won't be late. Arizona is allowed to count theirs early and most their mail ins are already counted.