Ronda is the best out of about 8 fighters in the world in her weight class who fight as a professional cage fighter. For every one Female mma fighter there is 50 + males. The talent pool is very shallow.
There is no opponents in female combat sports. Look at this for example at boxrec. There is 21 middleweight professional female boxers in the entire World. The # 10 boxrec ranked female MW in the World has a 1-2 record. The # 5 fighter in the entire world has a 7-6-1 record. If you are a female, have a pulse, and sort of train a little bit you could be a top 10 World ranked fighter .