It's unlikely that an importer or exporter is going to use Amazon for the freight forwarding outside its network. I guess Amazon only will end up handling shipments of its own or network sellers who significantly rely on amazon to sell their products, likely through LCL Consol box, putting a lot of smaller shipments into a single 40HC container., that's going to save them a lot of cost as well as give them tighter control over the shipment routing and transit time etc.
Other regular importers & exporters either in China or USA are never going to use it. Because of the reason mentioned above.,
An importer or exporter shares too much sensitive and critical information with his freight and customs agent., If I suddenly get involved in trading or in other words become their competitor its obvious no one is going to share the information with me.