All women secretly consider each other rivals?
It's an interesting statement for sure. Truthfully though, it's one of those things that's not as cross cultural as it may seem.
At first I thought "rivals, really?" as I thought of all my female friends, how they acted to each other, to my face and otherwise.
Then I had an epiphany; watch Japanese Anime for a quick update on how women are generally treated in Japanese society. From my apologetically non-experiential knowledge, I understand that Japanese women are not treated as equals with Japanese men, that being the case a Japanese women might feel that they are as strong as their male counterpart, and the 'rivalry' if you will, stems from the want of that said male counterpart.
What saddens me the most is that I'd come to understand about Bayonetta (haven't played the game, but have watched the Game Overthinker's interesting character analysis @http://gameoverthinker.blogspot.com/2010/02/episode-32-i-heart-bayonetta.html) is that I've come to know her as a representation of sexual domination in women. And that even with the creation of the character, shows a shift in Japanese sexism. (if only slightly)
Mr. Kamiya's comment then shows that he's either oblivious to the impact of his own creation, or didn't fully understand what he was doing in the first place when he created her.