[Leeland]

That could create a nice time-delay if you want to have truely powerful beeings emerge.
Say the soul of the mother imparts "what is right and possible in this universe" on the soul of the baby in the womb.
Now, if a soulless mother has a child, it gets a soul of it´s own, but is not restricted by information/rules a babies soul normally gets from the mother.
So the power of the baby is "unlocked" in a cosmic sense and able to grow in the first nine month like it was never possible before.

Therefore every baby born to a soulless mother gets superpowers!