Can be said for all monopolies. I am not arguing that Amazon is not successful. They are so successful that they are now showing monopolistic behaviour.
The MFN principle is enforced - but only for the same reseller. The same product may be sold in another channel under another reseller, Amazon cannot touch that. AliExpress is surely outside of that scope. Also, EU managed to "convince" Amazon to stop MFN in principle in EU countries, practice is different (they don't enforce it, but give credit breaks) - it's still being enforced in USA and subject to legal challenges: https://www.johnstonclem.com/news-insights/amazon-antitrust-...
The MFN principle is enforced - but only for the same reseller. The same product may be sold in another channel under another reseller, Amazon cannot touch that. AliExpress is surely outside of that scope. Also, EU managed to "convince" Amazon to stop MFN in principle in EU countries, practice is different (they don't enforce it, but give credit breaks) - it's still being enforced in USA and subject to legal challenges: https://www.johnstonclem.com/news-insights/amazon-antitrust-...