This seems like pure speculation, but if Delta club access is restricted to Amex Plat cardholders with the exorbitant fees that we're paying for it, I see no reason to keep the card.

We've already seen ridiculous devaluations from Amex (Priority Pass restaurants at airports) that has contributed to more crowded Centurion and Plat lounges. I'd choose a restaurant over a lounge in most instances if I was still able to.