IANAL but I don't see a judge deciding that AWS doesn't have a million competitors in every dedicated server host or collocation datacenter, even when AWS was the only cloud infrastructure provider. As long as antitrust laws don't apply, freedom of association is pretty unassailable.
Yes, they don't have a monopoly or even close to one in VMs.
Or video streaming.
ianal but I was under the impression that in the US you need to provide equal service to any customer, or else be ready to tread very carefully to avoid legal consequences. This doesn't mean you have to give a competitor special pricing, but I think it does mean you have to sell them your catalog listed products and services at list price, or else be prepared to head to court eventually.
Where did this impression come from? I thought basically the opposite was true: that you could do business with whomever you want, as long as you're not discriminating against a protected class of people.