To be honest I have seen women being like that not only in yaoi, but also in Shoujo, Shounen, yuri, etc...
I began to ask people if women were really like that there, not really according them... is like the mexican's Telenovelas, women in those soap operas are the worst but is not 100% reality...
Something they told me is that women in Japan search future husbands very young and they are very competitive (not as these manga level), because they have an "age limit" to get married and the society expect they get married and have children.
Watch "together with me series" it's a sexy boys love drama. And there's this amazing girl that basically helps them out and hooks them up. She's an amazing woman, who really cares for her friends.
With a few notable exceptions, all the women in yaoi are either:
A. Psychos
B. Total Bitches
C. Complete freaks
D. Old grannies
I love reading yaoi, but I wish the stories included more normal women and girls.
It's almost like the authors figure the female characters need to be really awful in order to explain why two men would get together.
Personally, I enjoy yaoi stories more when they include cool, kind, intelligent, and attractive women, even if they sometimes get their hearts broken. ☹