I used that scenario as an allegory. God did not literally shoot His Son to death, but He did kill Him. The Penal Substitutionary Atonement theology is correct. When Christ 'became' sin, God dealt with His Son in the same exact manner as if it was you or I.
God made him who had no sin for us, so that in him we might become the righteousness of God.[2 Corinthians 5:21]
There was a double imputation that took place. He was imputed our sin so that we could be imputed His righteousness.
Lets say you owe the bank 1000$. You deserve to pay it. And you don't have the money.
So a good friend of yours JAY says to the bank I will pay for it and he puts up 1000$
The Bank takes the 1000$
How much did the bank forgive you? ZERO. They didn't forgive you at all, they just took their payment.
For the bank to FORGIVE it just cancels the bill. Actual forgiveness means they would let you off despite ability to pay.
In other words your idea is like a pagan monster God. He NEVER forgives he is going to get his appeasement one way or another.
Matthew 18
23“For this reason the kingdom of heaven may be compared to a king who wished to settle accounts with his slaves.
24“When he had begun to settle
them, one who owed him ten thousand talents was brought to him.
25“But since he did not have
the means to repay, his lord commanded him to be sold, along with his wife and children and all that he had, and repayment to be made.
26“So the slave fell
to the ground and prostrated himself before him, saying, ‘Have patience with me and I will repay you everything.’
27“And the lord of that slave felt compassion and released him and forgave him the debt.
28“But that slave went out and found one of his fellow slaves who owed him a hundred denarii; and he seized him and
began to choke
him, saying, ‘Pay back what you owe.’
29“So his fellow slave fell
to the ground and
began to plead with him, saying, ‘Have patience with me and I will repay you.’
30“But he was unwilling and went and threw him in prison until he should pay back what was owed.
31“So when his fellow slaves saw what had happened, they were deeply grieved and came and reported to their lord all that had happened.
32“Then summoning him, his lord said to him, ‘You wicked slave, I forgave you all that debt because you pleaded with me.
33‘Should you not also have had mercy on your fellow slave, in the same way that I had mercy on you?’
34“And his lord, moved with anger, handed him over to the torturers until he should repay all that was owed him.
35“My heavenly Father will also do the same to you, if each of you does not forgive his brother from your heart.”
Notice the man has no means to repay but the lord felt compassion. He didn't say ok Ill give you a chance to repay neither did anyone walk up to pay. This is actual forgiveness in action. He has no debt.
What you are saying is God the father is incapable of forgiveness. Worst then that is the idea suffering is some how a currency to satisfy his sadistic glee.
God would never turn his back on Jesus.