This is an issue I didn't think about until I red this topic.
What induced me to think about it was "why did someone started to talk about it". The answer is: through the game, more or less 80% of important characters that are portrayed as "evil" are male.
Now, I know one shouldn't generalize when it comes to gender stereotypes. Reborn has a really complex story, and nothing is completely black or white. As the plot progreses, we get to know characters motives and backgrounds. Therefore, there's no such thing as an evil gender and good gender.
It's just that until we get to know about Lin, all Meteor admins and traitor gym leaders (dr Connal included) were guys. ZEL in body only but still. While the girls, while not weak at all, had to be saved by PC.
If one think about it, it does feel a bit off.
But if one thinks about it more, this "gender difference" is just a coincidence. Ame already said that the gym leaders were antagonized already from the League era. As for Meteors, when counting the characters I realized that we have an ideal 50/50 when it come to important characters (not counting PC, Adrienn and Shade). Before the Meteors were created, there was just more girls then guys in the league, so I think it was just to create some balance.
Soooo, after thinking about it and writing it down, I came to the conclusion that there's no gender bias in reborn.
Besides that, some female orderlies and cultists would be nice.