God bestows his favor on whom he wills.
Can you imagine what a world we would live in when the righteous thought to themselves, “I deserve your favor, Lord, look at all I have done!”? Yet we are unprofitable servants and we have only done what we were asked to do (if that). [Lk 17:7-10]
Of course, we do live in that world where people think this; it was a joke.
You are thinking from within the confines of the box that you have tried to put your own creator into. He will not be told who to show his blessings to, nor his curses.
Edit: Also, Jacob did not receive the blessing “legitimately” if by legitimate you mean “without sin”. That would be incorrect. Jacob lied.
18 So Jacob took the food to his father. “My father?” he said.
“Yes, my son,” Isaac answered. “Who are you—Esau or Jacob?”
19 Jacob replied, “It’s Esau, your firstborn son. I’ve done as you told me. Here is the wild game. Now sit up and eat it so you can give me your blessing.”
Again
20 Isaac asked, “How did you find it so quickly, my son?”
“The Lord your God put it in my path!” Jacob replied.
And again
4 “But are you really my son Esau?” he asked.
“Yes, I am,” Jacob replied.
Does anyone need evidence that lying is wrong? It is in the CCC. Jacob lied, an intrinsic evil in the eyes of God. That is indisputable.