If the same holds true for E+, why even have a companion benefit at all?
Yep. Delta has acknowledged that their customer behavior modeling (and realtime experience after the last devaluation) tells them that enough customers will want to avoid the uncertainty to pay up to C+. The management gamble is that the number who pay up will be greater than the number who book away to AA, UA, Jet Blue etc.
As a shareholder, this will be interesting to watch shake out.