Sorry if my misunderstanding of biology and pregnancy are grossly inadequate.
Pregnancy is not a one-way street, basically, you don't just get to input sperm and take out baby and the mother is irrelevant other than a tank. You can't increase viability while decreasing physical activity. You can't increase viability while eliminating language. you can't increase viability while keeping women in cortisol state of eternal stress. you can't increase viability when eliminating vitamin D. and on and on and on and on and on. and without even touching on the new discoveries of the profound feedback loops (negative and positive) that epigentics is unraveling.
You can certainly breed for "breeding" characteristics, like how the dunyain have obviously bred to select for multiples, but this will also simultaneously breed for smaller progeny. Given the immense nutritional deficiencies of what we know of the dunyain dietary, halflings is what they should probably be at this point.
Basically the dunyain use methods guaranteed to make conception extremely unlikely, to guarantee high rates of still births and miscarriages while somehow breeding male and female characteristics into vastly different outdomes in spite of all the interdependent variables that a common breeding stock would necessitate.
