This shouldn't really be the discussion. It's kind of a side show. She is an extremely accomplished fighter and deserves to be respected as such.
But...
He's absolutely right. She wouldn't stand a chance against any decently trained MMA artist. Men are indeed enormously stronger and strength does matter in MMA.
The bias that men tend to be physically stronger than women, pound for pound? The 50-100% estimate is probably an exaggeration, but from my quick glance at competitive weightlifting results, 25% seems well-supported.
According to the Wikipedia article of Olympic weightlifting world records, the 69kg men's record total lift is 359kg, while for women that record is 286kg. That's about a 25% difference.
Of course, world records might not be the best thing to look at, since the variance among the genders is probably different (although this discussion is about top MMA fighters, so it's fairly appropriate). Also, you can probably find very different numbers by looking at different weight classes and events.
Just a side note, "175%+" is actually a bit of an underestimate.
As an example, I'm 175# and can bench press 285# (3 whites) but I'm not a "strong male athlete" by any means.
Athletes who train for strength (linemen, powerlifters like GZCL) are putting up 2x their body weight or more, and that's just for bench press alone which is usually the lightest event.
Deadlifts and squats can hit 4x body weight which is just insane.
So your theory is that men are not almost always substantially stronger than women pound for pound?
It's not a bias, it's extremely well understood human physiology. Men and women are in fact very different in the strength department, men are vastly stronger.
The problem with saying "men are stronger than women" is that we're not dealing with men and women, we're dealing with a specific woman, and a potential specific man.
This is not about the aggregate, it's about the specific.
I would put Rhonda's ground game up against plenty of bantamweight men. Striking is a different story, of course, but god help any fighter that hesitates and lets her attach on to anything. Watch her spar with Uriah Hall, and how easily she takes down an extremely athletic man with a 50 pound advantage.
I don't think this fight would ever happen, but dismissing Rhonda Rouseys potential with biological hand-waving is an insult to everything she's accomplished. And I'm saying this as someone who doesn't even particularly like her.
In other cases, when talking about specific individuals--in particular, Olympic weightlifting record-holders--the gender difference is still very obvious.
MMA is extremely multi-faceted compared to weightlifting. There's a reason the Gracies dominated the sport for so long, and it had nothing to do with any kind of extraordinary upper body strength.
Let's be realistic here. Men are just way stronger and better fighters. It's the same story in other sports. For example Serena Williams: the best tennis player in WTA history by huge distance and she would be smoked by any men who is on ATP list even if overweight and smoking between games.