His job was to be the hatchet man, perhaps be unlikable in aggression, he did his job.
Cheney, in 2004, did not score well on the left .... he was arrogant, mean, condescending, would murmur over and variably interrupter .... Biden simply did his job.
He did it well. It is not Biden's likability numbers that matter (and they took a hit) (just as did Cheney's, although with Cheney they went from 1% to zero, even the bugger's hunting partners don't really enjoy the guy, from what I understand being shot in the face is not an endearing moment).