Eh it's not that great of a comparison.
But if you wanted to argue Rousey is the face of MMA right now, especially WMMA, I would agree with you.
I would put her at the Peyton Manning or maybe even the Tim Duncan level.
There is no way she transcends her sport and enters the cultural conscience like Tyson and Jordan and those other once in a generation type stars. She is John Cena to Hulk Hogan. The fans of the sport might know her, and a few others that may casually, very casually have an idea about the sport. But normal people really have no idea who she is or care one bit.
In terms of dominance, waaaaay too many people are 10-0 in combat sports, just the record is useless.
Brock Lesnar was closer in terms of notoriety and success. But I think Lesnar won't get that respect same as Rousey because the divisions were just too weak when they rose. And arguably with Lesnar there was the lurking shadow of Fedor. Rousey does have Cyborg lurking, but fans seem to care less about really seeing that fight. I would like to see it though.