I think it should honestly protect their bonus from all, seeing as there aren't any good prot bonus cards in the game. So archie would be protected from cancel modifiers and sledg would too. However, I wouldn't be against it working only for STOP opp bonus, if an actual argument could be made.
That bonus would literally make the clan unstoppable, unless all cards had a MAX power of 6 or lower. I hope (doubtfu) that the next clan adds a better dynamic which of a reason to use older cards again.