Don't agree with that. AMD nor Intel control kernel-level process of managing threads (aka the dispatcher) ... if that were the case, AMD and Intel would be able to do all kinds an special overrides to try and handicap each other.
Are you referring to "Intel Thread Director", if so that provides "feedback" to the OS in the hope it makes the optimal decision for the workload ... see reference
here. The OS is still very much in charge and Microsoft worked with Intel to ensure the OS was doing what they asked. AMD work with Microsoft just as much as Intel, but for some reason Microsoft didn't understand how to make the OS work correctly with AMD or it was an honest mistake or AMD got lower priority for internal resources that could affect the change needed.
But agree, one can't technically say "special relationship", perhaps a better description is Microsoft understand Intel better than they do AMD? It would be very difficult to prove favoritism, not impossible, just difficult.