I understand why Microsoft and Epic don't like this policy. it certainly makes it much harder for them to compete with Steam. But, that's business. Microsoft and Epic have very deep pockets. They can throw money at the problem and overcome it, if it's that important to them. Microsoft could effectively buy the exclusive rights to every game in existence and force Valve out of the market in short order, if it was that important to them. The fact that they're not doing it shows you that it's really not that important.
I wouldn't think differently no matter who the complaints were. But, it is particularly ridiculous coming from Microsoft. They could just buy Valve if it's that important.
Buying companies is a LOT more complicated than that, especially with what you are suggesting lol. For one thing, people aren't always just waiting around to sell their shares to someone with a bunch of money. Some people own shares that they don't want to sell, no matter how much someone offers. Others who would normally sell won't out of principle to a mega corporation. On top of person choice, let's talk government oversight: A republican administration would be all over one company trying to buy that many competitors out, let alone the current democratic one. Bethesda is one thing. But if Microsoft were to try to "buy the exclusive rights to every game in existence" they would be blocked before they even got to 15% of every IP out there probably lol. The guy in the White House who is constantly asking people where he is, what he is supposed to say next, and refuses to do press conferences probably wouldn't be on top of it, but absolutely this would have Bi-Partisan support to be shut down by Vice President Harris, Congress, and the federal courts.