1. Start a lawsuit against Valve rather than Dolphin Team as a SLAPP (Strategic Lawsuit Against Public Participation). Valve could then end up spending millions defending itself from the mad tyrant and the best case is it spent millions to confirm it was doing nothing wrong in the first place.
2. Tell all their 3rd party publishers to stop publishing on Steam, in order to continue doing business with them, utterly ruining Steam.
In both these cases, it has nothing to do with legality or the DMCA, which Dolphin Team's own lawyers have explained if you'd just read the article. It has to do with a big bully getting angry if it doesn't get what it wants, and is willing to throw its weight around.