I've been comparing the female division to the early UFC, but for a slightly different reason, but one that would still make Rousey into Royce...
There are so few female fighters on the big stage, and most of them haven't even fought at a UFC event yet, so we will end up knowing what each one is capable of and with a limited number of possible match-ups... Like how there was just Tank Abbott, Dan Severn, Royce Gracie, etc. in the early days, and of course, one of them being an unbeatable submission artist.
However, I'm not sure how much credence we can put into Rousey's skills since she has only had 7 fights, and only one of those in the UFC. The more she does it, the more everyone will be able to prepare for it. I'm not sure if she will be able to do what Gracie did now that MMA has evolved so much, or once the female division grows and attracts better fighters.
P.S. If someone would start a thread that takes an in-depth look at the female UFC roster so we can get to know all of them better, that would be really cool... Something like, "An Introduction to the Female Bantamweight Division" or "Getting To Know Your Female Fighters"