This is not a reasonable assumption based on my experience talking to women, and if it was, I don't understand how it would work in reality. Even if biological women preferred sharing the women's bathroom with trans men, rather than trans women, how would biological women know whether they were sharing the bathroom with a trans man or a biological man?
It seems much easier for trans men to pass than for trans women, so allowing trans men into women's bathrooms basically ensures that all men can freely enter them, claiming to be trans men.