Within the one subset of music that you're familiar with.I've found this to be very untrue... Vocals are one of the only places in the music world where a woman can be successful without being treated as a novelty. Female musicians are very common, unfortunately almost all of them are vocalists.
Women are underrepresented in Rock and, to some extent, Jazz music. Amongst Classical orchestras, there's parity.
You're only talking about Rock music. I can't admonish you for a lack of perspective, I suppose.