I'll also never understand that '20 points ahead' slogan. Saying 'any other leader would be 20 points ahead of Theresa May's mess of a Tory party in 2017' is one thing - not helpful, possibly, but legitimate.
What position would you have advised Labour to take that would have balanced urban remainers and small-town leavers just a year and a half after Brexit?
Corbyn was a poor leader who should have been clearer about Brexit - but I think Labour were stuck between a rock and a hard place then, and I don't think there was any way they could have been 20 points ahead then just because it would have been impossible to triangulate between those positions.
I think there's more mileage in a "fine, we voted for Brexit, but we don't have to do it this badly" position now, but I also don't think there's 20-point lead potential now. I think Starmer is actually being quite sensible in not making more of Brexit given that there's any easy riposte of "you didn't want it anyway, so you would say that, you don't understand your old core voters."