Old Testament sacrifices were accomplished by slitting the animals' throats so they would bleed to death. The blood was an important visible and literary symbol of their death--but their death, not their shed blood, was the point. When Scripture refers to blood it means death. Indeed, Jesus bled to death, fulfilling the Scriptural pattern.
This is not hard. To argue otherwise confuses process with outcome and is splitting hairs and sophistry. If your other arguments are no better, your ill-will agenda does you no honor.
Because the life is in the blood, when the blood is shed, then it is proof the life is gone, that death has truly occurred.
There could not be a better visible proof or guarantee that He was dead than to have His blood poured out. There could be no claims of faking His death then.
Can you believe the gall?