In Matthew’s version the crowd glorifies God “who had given such authority to men” (Matthew 9:8). Doesn’t Matthew himself read this as delegated authority, not divine identity?

This is the best text for the agency reading. Matthew 9:8 records the crowd’s reaction, and crowds in the Gospels regularly misunderstand; Matthew does not endorse their inference. But grant that Matthew allows the delegated reading. It still leaves the scribes’ own reasoning, who can forgive sins but God alone, unanswered except by a demonstration. Jesus does not say God has authorized me to announce forgiveness; he says the Son of Man has authority on earth to forgive sins, and proves it. Whether that authority is delegated or intrinsic is what the rest of the New Testament evidence is meant to settle, and this scene is one strand of it, not a proof on its own.