I do agree that head-to-head polls are useful and informative. The fact that the time is so far off mitigates that, but doesn't completely cancel it out, and the same thing is true of the fact that Biden has a history of fizzling.
But the one we were shown here failed to show Biden's results being better than everybody else's, which was the claim, because it was only Biden's numbers, and a simple search for something like "Trump Bernie polls" will turn up a pile of results on that matchup over the last few years, which consistently show a better gap for Bernie. (That was always one of the issues for the Bernie Bros: while a standard claim among Hillaryites and other Democrats was that she had a better chance of winning because of course someone who would actually do stuff to improve the country could never possibly win and you had to be a Republican in disguise in order to have a chance, absolutely all of the actual data said the opposite all along, and was completely verified on election day.)
The current difference between B & B is smaller than I expected, given the fact that Hillary always waved between +2 and -1 or so and Biden is simply Hillary II, but the difference is still there, and I expect it to grow because Biden will Bidenize again. At best for the "Biden's more electable" side, it could be seen as a rough tie. The idea that he's the most electable can't possibly be coming from the poll data. It can only be another round of the Democrats' same old "our side can't ever really win so we need somebody just like the other side" myth which has never worked in my lifetime.