Offhand, I get two rather general impressions from the mammary-related fan-flack: (1) people are far too ready to define characters by body type, and vice versa, and (2) 'tis a strange line being drawn when you can say: "Morph this animated equine into a human(oid)? Sure. Give said equiniod anything above a B-cup? NOW it's weird!"
That said, athleticism hardly equals waifishness-quite the contrary in many disciplines. Consider this my vote of support for Amazon!RD.
ain't it amazing how MyLittlePony *hears the theme song in my head when typing the name* is... well... they made the amish pure lifestyle POPULAR with the disgusting inhabitants of the furthest reaches of the internet? people who would have sex with a birds nest, now respect little animals? it's mind boggling if you ask me.
This reminds me of Roberta in "Now and Then", although she didn't really have much of a chest yet and was more trying to stop her chest from growing, haha. I admittedly like to think Rainbow Dash would be shorter and athletic, but "athletic" covers a lot of body types and I think runners tend to be taller? This kind of depiction easily lends itself to imagining her playing soccer or rugby or something!