Then, I suppose, "your sins are forgiven " (absolution) and "their iniquities I will remember no more" is for naught. An eye for an eye, or, as you say, "measure for measure" is what "cheapens," that is if the NT is any measure at all.
Thus, "Do unto others as you would have others do unto you."
The sinner is called to repentance and God promises forgiveness as I recall. Once forgiven, the believer is called to do unto others and he would have others do unto him. You do not forgive those who trespass against you by punishing them after forgiving them; you forgive others so that God may forgive you, or at least that's what I was taught.
But our respectful traditions differ in that regard, as both differ with regard to the Protestant way of looking at it.
"Forgive us our trespasses as we forgive those who trespass against us" strikes me as acknowledging that we gain remission from our sins in the measure we forgive our fellow trespassers. This is "measure for measure," but not of the "eye for an eye" type. It is imbued with the spirit of Love. God wants us to love one another, and blesses us when we do.
Or so it seems to me. FWIW