That was quite fascinating! I do like your reasoning, and I'm glad you made clear it truly is just a marketing thing. But I would like to suggest that it's completely believable that females of a certain species (Skakdi) would be more aggressive, since we see that in nature here, namely in insects,aand in several mammals, especially lions. Since Skakdi are almost animalistic the way I understand them, it wouldn't be very far fetched at all to call the females more aggressive. I put forward a reason for all the water Matoran and Toa being female is that water, as a whole, is calm and gentle. Since all other element's members reflect their element, and Toa especially magnify it. Kopaka is very collected and chill (pun not intended), and Tahu is hot-tempered and headstrong. Therefore, it would appear that the general female personality and temperance reflects water more than any other element.