Monopoly regulations are to prevent unfair misuse of a market position - nothing to do with "rights" to sell. See AMD Intel suit:
https://en.wikipedia.org/wiki/Advanced_Micro_Devices,_Inc._v._Intel_Corp.
AMD has claimed that Intel engaged in unfair competition by offering rebates to Japanese PC manufacturers who agreed to eliminate or limit purchases of microprocessors made by AMD
Sure you could buy AMD, but you would't get a good deal on Intel CPUs - and that is monopolistic abuse.
In this case I think it could be seen as collusion between Apple and Amazon to further eachothers market share - and thus it's not necessary to prove a "right to sell", but rather to show that this prevents a fair and open market.
NB IANAL.
Apple's prices and requirements with Amazon are no different than they offer to other resellers, so the AMD example doesn't apply here. In fact, it's that hard price parity that upset so many legacy authorized resellers because they had no advantage at all, and the additional price breaks for large-volume deals are miniscule compared to other OEMs. The resellers with an actual sales force have an advantage for any larger sale as Amazon is a passive marketplace, but how many companies are buying $1M in MacBooks and how often?
The resellers in this article, however, seem to me to be upset that they are also also not allowed to ride a train using Apple's brand while passively sitting there selling virtually nothing compared to established resellers.