It is the purpose of copyright, explicitly, to incentivize creative work with the promise of monopoly power over its distribution. So it's a bit disingenuous to assert that microsoft is not a monopoly because other game companies exist.

Tech companies have long understood, and in fact may be entirely predicated upon the understanding that you can leverage one monpoly to create another.

If I make a game that can only run on your platform, then you gain a monopoly on platforms that can run that game. These platforms then become not fungible, and therefore de facto monopolies. There is a certain amount of "we haven't tried to port our game to other platforms", which probably shouldn't be an explicit violation of the law, but entering an exclusivity contract with a game studio is, in my opinion, a pretty clear restraint of trade.