At this point we've got four flat-chested girls (Marie Rose, NiCO, Nagisa, and Kanna). Yes, DOA has had plenty of buxom women, but at least that was a bit of a staple for the series, what set it apart from most other fighters.
And quite frankly, I don't really care about beauty standards (when something's relative, it's inherently meaningless, so why bother to care anyways). But I do realize that the closest beauty standards have to an actual standard is economic factors, and if buxom women sell, well, they're the beauty standard, whether one likes it or not.
Besides, DOA6 tried to change up that formula for one reason or another and... well, it ended badly for that game, let's leave it at that. And just as an FYI, I can tell the faces apart regarding those girls.