I think you are doing "other people" a bit of a disservice. The extension of the above suggests that there was a potential policy that wasn't going to be an electoral disaster. And that potential policy didn't exist.
Your posts suggest that had they taken a more "leave" position then they keep their leave seats but for some reason don't lose their remain ones, and thus perform better. And there is nothing to suggest that's the case.
As you've rightly said, they were placed in an impossible positon. Which isn't hindsight, I don't believe anyone claimed otherwise last Autumn. They (rightly, in my opinion) decided to go with what a majority of their MPs, members and voters wanted rather than a minority. It wasn't going to win them the election, but going with "we need to win Mansfield, Stoke and Grimsby and the people who vote for us there are racist statue-defenders, so we're just going with whatever they want" was no more viable an election strategy than what they chose.
For all the Miliband reports, the story of the 2019 election is that Labour didn't have a pragmatic faction, willing to prioritize the success of the party over their personal position on Europe.
So (a larger number of) Labour leavers prioritized Brexit, (a larger number of) Conservative remainers prioritized the Conservative party.