That doesn't really change anything. The customer interaction is with Amazon and they own it including paying for it either with Prime or directly.

Those third parties likely owe pretty much their entire business to amazon. When a company can't exist without a specific client, is it really a third party?

I think delivery companies may vary - in my area, some deliveries are still completed by the national mail, major couriers, however small (and often incompetent) carriers are starting to.

The reason for my comment was that my experience receiving a shiny package doesn't really overlap with what employees are being put through. Both reflect poorly on Amazon, the conversation about employees is a valid on it's own as there are avenues with Amazon to already complain about poor delivery and have a recourse.