I disagree, because John 20:23 speaks directly to the issue, while Mark 2:7 is a rhetorical question posed by the Pharisees, that Christ chose not to answer in sufficient detail right then and there. The relation to the question, can Christ delegate the power to forgive sin to others? -- is only lateral in Mark 2:7
I was going to use your argument to support mine. :) I see it as significant that Jesus did not lift a finger to correct them after Mark 2:7, even though it was clear that He was reading their thoughts. He corrects them on everything else, why not this? I don't see the thinking of the Pharisees as being rhetorical, they were looking to nail Jesus for blasphemy (perhaps a poor choice of words), and in their minds this was the ticket.