ultimately the market is behaving as if the threats are sincere so whether or not Valve would follow through is irrelevent to whether the presence of a policy is an exhibition of monopolistic power

Courts have interpreted the anti-monopoly portion of the Sherman act, which governs antitrust law in the US, to mean that monopoly is only unlawful if the power is used in an unlawful way or if the monopoly was acquired through unlawful means.

The need to see an actual example of a game being delisted for violation of the policy is a weirdly high standard of evidence

As a smoking gun, I don’t think it’s unreasonable to ask for something like that.

If it’s a policy Valve denies and the only evidence of it existing is a single reply in a forum somewhere, then yes, I’m skeptical. And given that there are examples of companies that were willing to break explicit, defensible policies, why aren’t there examples of companies who broke these? Unless the plaintiffs bring in multiple witnesses to testify that this was the policy communicated to them or something along those lines, I can’t see the evidence that they did have this policy being more compelling than the fact that there’s a complete lack of evidence that they ever acted on it.

To be clear, I’m not saying Valve needs to have said that was the reason. But it certainly needs to look like that was the reason. If Valve can’t provide a valid reason for the termination, then that’s very compelling, and even if they can, it’ll come down to which is more believable.