Firstly, I’m not sure that this argument holds. There are also remainer-Tories. If you add up the votes from last night, pro-remain parties got 40.4% of the vote, hard-leave parties got 34.9% of the vote, Labour got 14.1% and the Conservatives 9.1%. Labour are leaving a lot of votes behind if they continue to annoy the remain voices.
Secondly, it goes beyond strategy three years after the fact. I feel that Corbyn has failed the country by refusing to discuss or debate Brexit in the years following the referendum. That firstly allowed Theresa May to frame the structure on which we would leave (her red lines that have got us in this mess), and has since meant that the debate has mostly been fought from the right of those red lines, bringing us closer and closer to no deal. If the debate was instead May’s red lines vs. Corbyn demanding a softer brexit to protect the economy (potentially with a second referendum to pass it), we’d be in a completely different situation. His indifference to the situation is maddening, and has given the debate to the loons on the right.