This certainly was the belief of the Hebrew/Jewish people. However what this does is to impose human limits on God. God has no limitations and can certainly forgive without the shedding of blood.
Micah 6:6 With what shall I come before the Lord, And bow myself before the High God? Shall I come before Him with burnt offerings, With calves a year old? 7 Will the Lord be pleased with thousands of rams, Ten thousand rivers of oil? Shall I give my firstborn for my transgression, The fruit of my body for the sin of my soul? 8 He has shown you, O man, what is good; And what does the Lord require of you But to do justly, To love mercy, And to walk humbly with your God.
I am convinced that all God requires for the forgiveness of sins is sincere contrition. So, in answer to the OP, I no longer believe that the death of Jesus was substitutionary atonement.