Either one alone can separate nature from nurture.

In what way? As knb mentioned above, parenting has a direct effect on e.g. what language you learn. On the other hand, parenting has zero effect on, for example, the color of your eyes. So you have to first specify what variables you're looking at.

And they both show the same result: 50% genetics, 0% parenting.

I hope you realize that this is an extremely strong claim.