Well if you have an argument for your the case, I'd like to hear it. My case is the result of calculations.
I'm assuming everyone knows this, which everyone should, but in case there's any misconception, % rate buildings have diminishing returns; the higher the proportion of the building you have, the lower the rate an extra unit of it will give you, or for effect rate y on percentage x, dy/dx->0 as x->50. That accounts for the tendency for the split to become more even, even if one is clearly better than the other at initial levels.