I think Macromastia is bugged to act like Overall gain. The description of characters with Macromastia doesn't seem correct.
Not all characters of the same Body Shape are exactly the same!
So you might have met one that is not that extreme.
I think the uniqueness of every character comes out really well.
The procedural generation is one of the strongpoints of second helpings - no two characters are the same! You have to be very lucky to meet exact twins ;)