The female first officer myth was debunked long ago. NBC didn't like Majel Barrett not the idea itself.
Where do you people get this non-sense?
Gene Roddenberry himself cited many of these cases of network prejudice. Was he lying? And who are you to say he wasn't?
Google is your friend. Or you could read Inside Star Trek
which was co-written by the Desilu executive (Herb Solow) in charge of the production of Star Trek
, it's pretty well documented.