I think that you all are vastly overestimating what Harry is able to do. I know that TC said that Harry is willing to go all-out, presumably even breaking the laws of magic. However, if his goal is information, he wouldn't just be immediately blasting Marcone to powder.
There is a reason that Harry is more afraid of Marcone than most anything else Supernatural. He has an incredible level of planning, preparation, and resources. He's also incredibly smart. And Harry, despite all his power, is still a glass cannon. One unexpected bullet ends him, like anyone else.
Is it possible at all that Marcone entered into this meeting with Dresden without a way to get out if the worst case scenario happened? Very unlikely. They're going to treat a Dresden on assault with the maximum level of threat, which means that there's no holds barred. Their goals are to have Marcone break contact in order to escape. And thinking that Marcone doesn't have other guards nearby ready is just foolish.
Harry and Molly going against Marcone is like two Queens trying to take on a chessboard with one King and a full assortment of Rooks, Bishops, Knights, and Pawns. No, individually they're not as powerful. But they'll out-maneuver him.