I don't see how Amex could have made this decision. From the customer's point of view, the 72-hour penalty is highly salient. Increased availability is largely invisible. Even if there is a net benefit to them, customers will not see it that way.

Customers will hate this change, especially those who learn about it only after losing their miles. They WILL cut up their Amex cards. No, Amex did not ask DL to do this.