Delta says that nearly 1% of GDP is currently being charged to their Amex cards, why would they risk this? A lot of Delta cards are going to be cancelled since they no longer have unlimited or any access to Sky Clubs, and since the thresholds for earning status are so high.
There will be some people who double down on their Delta Amex cards, but at the end of the status chase if they can put hundreds of thousands of dollars of spend on those cards, they will have… Delta SkyMiles instead of more valuable rewards currencies they could have earned. The opportunity cost is high!