I use this set with changes to the running game and a slight boost to AI coverage and the AI QB usually completes between 60%-70% of his passes. Even though I sometimes switch defenders on run plays, I never switch on passing plays. Sometimes (but not often) I hold subpar QBs under 50%. But that is probably a function of being in my 3rd year in a offline CFM.
Your issue is either a personnel or a playcalling one.