This isn't about what you're trying to make it about, yes Kojima made a perverted tweet, I'm not arguing against that, I'm just trying to show that this isn't his perverted design decision to create a "boob physics" feature, it's an action figure decision to increase poseability and nothing more.
Of course it would be less offensive if Quiet was wearing anything other than a Bikini...but since that's her design, they have to play ball.
I tried to take some pictures to show the effect (in the name of science of course.....)
It's much harder to notice on snake since he's in a thick sneaking suit as opposed to a skimpy bikini, but it's there.