Duh. The verse still describes the viewpoint taken by the people who had not yet known the divinity of Christ.That point is unrelated to the fact that God gave Jesus the power to forgive sins. That means Jesus didn't inherently have that power.
The verse does not say God gave this to Jesus. It speaks of God giving such ability to men, but there was only one man who forgave sins. So Matt 9:7 gives a commentary on the people's vantage point.
I guess you start with the weakest arguments first and then try to build up from there. I also can share a little secret. Those who gathered together to talk about the full identity of Christ Jesus had that verse available to them too.