What's this based on exactly? I mean, is Bethe Correia on that list? If so that's pretty hilarious a part-time fighter who has only been training any kind of martial art for a grand total of 3 years is considered one of the top 20 female fighters in the division.
To put that in retrospect, that'd be like if I decided I wanted to be a basketball star in my late 20s and became one of the top NBA players in the league with 3 years of part-time playing and practicing the sport.
Women's MMA is pretty illegitimate. Nearly all of them are into it part-time and have very limited extensive backgrounds in a starting martial art.
The rankings are based upon win record, win record of opposition and ranking of opposition. And while nobody would argue that WBW isn't weak compared to the more developed men's divisions, there are a lot more women with combat sports backgrounds, MA backgrounds and actual ring experience than in featherweight.
Featherweight has women with even worse records and less experience than bantamweight. And Cyborg has defended her belt in a significantly worse division, fewer times, against even lesser talent.
Correia would probably be a legitimate top 5 in featherweight. Nobody actually believes that Correia is a competitive top 10 bantamweight outside of the UFC official rankings which are a load of bunk.