What rpg is trying to tell you is that you need to be found a monopolist in a court of law first, before certain monopoly rules apply.I'm sure its against the law to do so. After all MS had a monoply in the OS market and used that to push out web browser competitors.
As long as this is not the case, the rules are much, much looser. Ergo, it's pretty much certain that it's not against the law.
With ~30-something % of the GPU market, you'll have a hard time indeed to first prove that they are a monopolist.