I think Amex's higher merchant fees leave plenty of room for profitability on the ED.
Paying out 2.4 MRs on groceries and 1.2 MRs on everything else really isn't that expensive for Amex when they have a low-risk pool of customers.
I don't think MRs are going to get much better. Keep in mind they just nerfed the MR-to-Avios conversion rate, which makes short domestic American Airlines flights more expensive. Not offering credits on Small Business Saturday makes light-spend accounts less of a rewards drain.
ED is an MR-earning card without an AF, but it's also a cheap-looking card without the distinctive appearance of charge cards. It's the charge cards where they promote the image of luxury. ED is also not the first MR-earning card with no AF. There was Blue, and Blue cards are now being converted to the better ED.
From a value perspective, PRG and Platinum, and arguably Zync and Centurion, are generally the better deals among charge cards.
I don't know what will happen to Green and Gold. CSP just blows them out of the water value-wise. Plus, people who need to feel special with a card with the Amex Centurion on it are going to be vulnerable to CSP's metallic seduction.