The election being lost primarily on Brexit is a myth. The Lib Dems didn't gain enough Labour votes to get any more seats. As for the BXP stealing Labour votes, well, here's a good analysis:https://www.reddit.com/r/ukpolitics/comments/ear3yf/marginals_where_bxp_votes_made_the_difference_how/ …
You just contradicted yourself. If the number 1 reason is Corbyn, then Corbyn was primarily the reason for the loss, not Brexit as you claimed.