I don't really doubt that mediocre men often fail up - I've witnessed it myself. But this isn't a great title, the conclusion that mediocre men fail up is from the qualitative part of the survey in other words - women believe mediocre men fail up. Which then highlights the obvious point, maybe mediocre poeple fail up, and you only notice it because men are much more likely to go "up" at all. I've certainly also witnessed mediocre performing women in senior positions, but since there are such a tiny number of women in my field, I would be much less willing to draw that conclusion.