I think the real devaluation here is not the loss of using SWUs on AF/KLM (which is something the vast majority of SM members never used), but the loss of (or reduced) availability of AF/KLM Business awards which is something far more SM members have used.
Delta TATL business award availability has always been bad, the saving grace was access to AF/KLM seats. And I believe that's what probably drove AF/KLM to do this... they had to be wonding why they make their seats available for awards when Delta makes practically nothing available. Delta's leadership of the alliance at work...