The Williams sisters lost 6-1 and 6-2 to the 203rd ranked male tennis player. The woman's 100 meter sprint record, a steroid time that no one woman has come close to in 30 years, is regularly beaten by high school boys. The Canadian national women's hockey time, four times Olympic gold medalists, plays practice games and loses more often than not against local 15-17 year old boy's teams (who aren't allowed to body check). The Swedish woman's soccer team, Olympic bronze medal winners, practiced and lost against 16 year old boys teams.
And you think Rousey is beating low ranked adult males? She'd have a chance against trained high school boys in the 15-17 year old range (there's a reason that the Canadian woman's hockey team went for that range, but doesn't practice against 18 year olds).
On the other hand, she'd tie most untrained men into knots all right. WMMA is great, I like the style and the dynamics. But pretending they're beating men is doing WMMA a disservice, and is often said by people who want to get rid of WMMA by forcing them to fight men (ie if women are competitive against men in sport, why have separate women's divisions?)