Whilst I agree with your conclusions, I am not sure about the analysis (i.e. May didn't perfom well in the election because she couldn't be arsed to turn up to the debates). It was Labour's campaigning that killed May's campaign in the water with the social care tax (or whatever it was called). She didn't want to turn up to the debates, because by that point in the campaign cycle Labour had turned the debate so harshly on May's policy and character that attending was a zero-sum game for them.
Although it's cliche, Labour are a campaigning party and Boris is a very good candidate to campaign against. So I don't think the result will be as devastating as polls currently predict, but yes a GE now would be bad for Labour.