Essentially. Look at early UFC. It was a new sport. She was one of the first one's in. She had one special skill and a lifetime of training. Most women don't have any fight training. It's not like dudes coming over from wrestling or boxing. She beat a bunch of truck drivers and bus stop hobos. Then the sport grew up and she started fighting people who had some skill and she got totally exposed. She has no legacy. She's the equivalent of a caveman artist. Yeah, nice job etching the stick figures. It's not a masterpiece.
It may be true that she didn't fight anyone of note - I don't know. But this same kind of progression is what happens to every other immature strategy in competitive games even if the competition is reasonable and otherwise good. I follow a lot of eSports, where metagames are often much more fluid, and this kind of thing happens all the time. Someone discovers that a unit or ability can be used in a way that makes a very particular strategy very good, and until a stable counter is developed, it dominates.
Rousey probably got over-famous with her one special move, that's for sure. But man did she know how to do that one special thing well.
The odd thing about all of this, really, is that it dominated for so long and to such heights. There already was a "one true style" in Men's MMA that could have been reasonably copied in Women's MMA, because (at least, as near best I can tell) the sport had already dealt with pure grapplers long ago.