Speaking just for myself, I will admit that this one is more difficult to interpret as to "match" the rest of my theology. I don't feel secure enough to pronounce a slam dunk, as I would in other cases. :) But ultimately, we have a plain meaning apparent contradiction between this and Mark 2:7. Something has to give via interpretation. Naturally, we will both choose the interpretation that matches. And, I think that to an unbiased judge, a credible case could be made for either view.
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