Neither Jon Lansman nor the Unite Establishment makes basic strategic errors.
Either Lansman will become General Secretary of the Labour Party, in which case, "We're not in the pocket of the unions."
Or Jennie Formby will win, in which case, "We're united around Corbyn, but we're not dominated by Momentum."
If one or other had not bothered, then the Right might have put up. It would have lost, but this way it will not even have that.