And how is performance measured?

Aggressive behavior is considered admirable in men, and deplorable in women. Many women I know have noted comments in their performance reviews about their behavior - various words that can all be distilled to "bitchy".

And then you take your experience, connections and expertise to leave and start your own company where none of this happens.

But is that what we see in real life?

I don't have data or sources at hand, but I'd bet top dollar that F-M ratio among employees is much more lopsided in male favor among founders[0].

[0] Not using the word CEO, because that can be appointed for somewhat arbitrary reasons.