The cartel can give 0-confirmation transactions to its customers, because these are going to be repeat customers because the cartel covers so much commerce.
Everyone can give 0-confirm transactions to their customers. That's a question of business risk, not capacity. It happens now. Please search for the fast-transaction problem and/or the vending machine problem.
Don't play dumb just to obfuscate the point.
The point is the cartel
doesn't have delay transactions for its customers when it withholds them from the other miners.
The nature of the protocol requires that the cartel delay transaction processing for it's customers
because it withholds them from other miners. There is no way to avoid it! That's what you can't wrap your head around!
You still didn't get the point.
The customer will never care that the transaction is delayed into the blockchain (delayed until the cartel's mining servers wins a block in the proof-of-work), because Amazon will give their customers 0-confirmation access to what they purchased.
The merchant will care. He will not get paid until the transaction is processed. If the transaction is withheld from the majority of the miners, that opens an opprotunity for a double spend attack
after product has been shipped. This will harm merchants directly, and they will either not accept bitcoin transactions via Amazon at all (nullifying your trhoery altogether) or only accept bitcoin transactions with the added garantee from Amazon against double spend fraud. This will hurt Amazon.