[rick404]

I always found the concept of 'evil being proportionate to breast size' entertaining.

As far as dress goes: Classical good are typically modest, while scantily clad or "loose" woman are often associated with wicked or evil ways.

Woman who use aggressively use their sexuality in obvious means can be seen as form of intimation. Good and heroic characters tend not to intimidate.

With stuff like Sailor Moon you are dealing with young girls fighting mature women adversaries so you have innocence as the defining good. Sexual maturity is the end slayer of innocence and is very often the adversary in magical girl style media.