Genetic i see your point , but:
Yeah nandrolone in its unaltered state may be a stronger androgen with superior binding activity than test but if the finasteride was not used then the excess test would be broken into DHT which is slightly stronger than nandrolone(example in your post), and the nandrolone would become less harmfull DHN.
So now instead of the unwanted nandrolone strength we would have an unwanted DHN strength.
A catch 22 in my books chief!
That said , if we really wanted to clutch at straws , the finasreride use option would just come out the victor - If we are correct in assuming that DHT is slightly stronger in action than unaltered nandrolone!