No, I'm not comparing Men's Bantams/Flys to the entire Women's division, I'm comparing them solely to Rousey.
And them having better striking defense than most women (none) is irrelevant given the number of strikes thrown vs landed and the number of opportunities to land a KO.
Let's put it this way, Rousey throws few strikes per fight because her fights are so short. The men throw a LOT more strikes, ie, they would have a lot more opportunities to put their opponents in trouble and have a shot at a clean KO.
Now, if you're arguing that the difference in defense is SO vast that they don't have the opportunity to throw a clean KO over a period of far more minutes with far more strikes, that's what I'm not fully buying. A clean hook/uppercut/cross is clean no matter how you cut it, and if appropriately placed with reasonable power should result in a clean KO.
And I have issues with the "defense" argument because these guys aren't all fighting the top of their divisions. They fought through the lower ranks where the level of defense is lower.
Given that striking defense in MMA in general is sub-par, we're not talking a division full of Mayweathers we're talking guys with ample opportunity to land a clean strike.
It's a math thing if you see what I'm getting at...