...maybe. We've got the same problem with Tarquin that we used to have with Xykon; I.e. "Is this really his 'A' game?"
Tarquin could easily be holding back just to make it interesting and/or not kill all of his son's friends. Yeah, it's not "proof", but fundamentally I don't think he wants to win this one. He certainly doesn't want to wipe out the order. It's hard to picture him putting himself in a situation where he needs to rely on Nail for all things Snarly and/or dealing with the big bad.