The Brexit Party standing down where Cons won in 2017 certainly helps Cons *defend* seats. But Cons didn't get a majority last time, and they need a majority next time. They need to gain seats. And BXP standing against them in Lab marginals hurts their ability to *gain* seats
To put it another way, there's no magical difference between Walsall North (Con held marginal, 74% Leave) and Stoke North (Lab held marginal, 72% Leave). BXP standing down helps in the first, and would help in the second too. Not sure why anyone would think otherwise.
And, lets' remember, this is an election where Cons are on the *offensive* not the *defensive* - if there is a net swing to them, then we shouldn't expect them to lose many seats they currently hold anyway. And those Lab Leave marginals are their key target territory.
(all that said it may paradoxically help Cons in seats least associated with Farage- strongly Remain Con seats where they are fending off a strong rise in Lib Dem support. Consolidating their Leave support in such seats will help keep them blue).
