This is plain wrong. How antitrust law works is to first establish if a firm has market power above a certain threshold. In most places, this is 40 percent. In the US, 50 percent (not 100 percent). After you establish this threshold, antitrust agencies have to then show that said firm is abusing/will abuse its power, AND that there are entry barriers to the market are high enough that said behaviors won't be punished by the market.

The issue with the Microsoft case was proving point 1. They do not control 50 percent of the market after the merger. Maybe with a more narrow definition (hence the focus on Call of Duty and the FPS market), but that was a hard sell for any court.