The funny thing is, if you look at Bruce Timm's artwork, he would seem to agree with you. Well, as far as smaller cups go anyways...
https://f95zone.to/threads/something-unlimited-v2-3-6-gunsmoke-games.326/page-1448#post-8121931
The material in the first link I shared in the post above pretty much sums it up. I know that big boobs in porn are a popular trope, but variety is good too.
As for 2x4 gals (i.e. minimal waist curves), despite being more 'realistic', well that's a different thing. I don't mind impossible curves, and neither did Bruce Timm... I think he found a nice balance there between impossible waistlines and 'more common' boob sizes.
Of course, the artist that does SU is it's own thing, but it obviously is trying to invoke Timm's style, so it'd be nice to see a few gals with smaller flotation devices. Of course, by exaggerating the bustline, this helps make the art used in SU a little more unique and less of a 'copy' so there's that I suppose.