Biden is up 5 points in national poll averages over Clinton in 2016 at this same date before the election, that's a lot. Only up on Clinton by 0.4% in top battleground states though. Polls underestimated Trump in last election though, guess we'll see.
Well, if it means anything, recent polling (just released today) shows that Biden is leading in the 3 main battleground states (Mich, Wisc, Pen.) up between 8 and 10 points, depending on the state. His lead in all 3 states has increased from a poll by the same organization a month ago.
https://thehill.com/homenews/campaign/522718-biden-stretches-lead-over-trump-in-mich-wis-and-penn-poll