The point is that saying “they wouldn’t have won if they didn’t do X”, in a context where you are trying to say something useful, implies that X is some special thing that was only done by them, not that X is something that everyone does. Nobody says “Trump would have lost if he had failed to breathe”, because everyone running a campaign needs to breathe and saying that you don’t win if you don’t breathe is obvious, trivial, and tells you nothing special about Trump.
And “the pro-Brexit campaign did special things which the anti-Brexit campaign did not also do” has not been well-supported here.
I think the comparison in the case of Cummings and Brexit is to what other pro-leave campaigns would have done, rsther than to no campaign at all.
The point is that saying “they wouldn’t have won if they didn’t do X”, in a context where you are trying to say something useful, implies that X is some special thing that was only done by them, not that X is something that everyone does. Nobody says “Trump would have lost if he had failed to breathe”, because everyone running a campaign needs to breathe and saying that you don’t win if you don’t breathe is obvious, trivial, and tells you nothing special about Trump.
And “the pro-Brexit campaign did special things which the anti-Brexit campaign did not also do” has not been well-supported here.
Well according to the article, he and his team did do special things. Of course you may not believe that, but he presents a plausible narrative.