Need some hard evidence/research to back this up.  If people are just relying on impressions, that is pretty unreliable.  Evaluate a large, random selection of executive job appointments.  Have someone independently judge the potential of each job for success and failure before the hire of a new person.  See what gender the new hire is.  See if there is a correlation (controlling for things like age, past experience, etc.)

Aside: if women were never thrust into thankless roles, that could easily be interpreted as sexism too.