I think that if you had hypoplasia, you never would have had a baby who gained >1 oz per day. Nor would you be able to pump 12-15 oz per day. Did you ever take a look at the Shape of a Mother website (http://theshapeofamother.com)? I like it because it shows a nice sample of the various types of bodies and breasts that do their jobs just fine despite not being the "perfect" shape.
I don't know anything about the heritability of adrenaline and oxytocin levels. But you know what we definitely do get from our families? Anxiety. If you are raised by a parent who is a stressed, anxious person, there's a good chance you'll be similar.