I think this might be the reason for the strength disparity. Tasks that require strong people tend to be more dangerous but a sensible tribe leader would send the strongest to do these tasks whether they are male or female. A tribe where the strength balance leans female will grow slower than a tribe where there is equal distribution which will grow slower than one with male balance. This selection effect would cause evolution in that direction.
I think this might be the reason for the strength disparity. Tasks that require strong people tend to be more dangerous but a sensible tribe leader would send the strongest to do these tasks whether they are male or female. A tribe where the strength balance leans female will grow slower than a tribe where there is equal distribution which will grow slower than one with male balance. This selection effect would cause evolution in that direction.