Wikipedia search suggests some cultures don't care much about breasts at all, what you can consider weak evidence against Paleogenetic explanation.

Weak, yeah. After all, Westerners consider the face to be a great part of a person's sex appeal, and it's very important in sex (kissing, oral sex, etc.) - yet they don't cover it up. Do they not care?

What's really needed is data showing that breast size or proportions are uncorrelated with reproductive success, or at least with ratings of attractiveness.