As much as I am defending the notion that Rousey could beat a man with which she had a good matchup, the assertion that she could beat a top male champion is indeed far-fetched.

As has been mentioned all over this thread, sexual dimorphism is a real thing, and not just something men made up to repress the lowly women.

A strong, fierce, dominant fighter can absolutely be female. A strong, fierce, dominant fighter that is female and that could beat someone larger is exceedingly unlikely, and has absolutely nothing to do with sexism whatsoever.