On to the main point, because this thread had nothing to do with McDaniels or Shanahan no matter how hard anyone tries to pound that square peg into a round hole, I am convinced that the problem is twofold;
A) Pass patterns are too short. They are too focused on moving the chains rather than scoring. Moving the chains is a means to an end, not an end itself. The Saints kill you with 20+ yard scoring passes, and I don't think their players are that much better than anyone else's.
B) Dink n' Dunk passing has replaced too much of the running game (see above). Or rather, it has tried to. It won't work once you get down close. Theoretically, a screen or hitch is just a long handoff - we keep hearing that - except that it really isn't the same thing at all. Once you get into the Red Zone you have to have a believable running game, even if you choose to score via the pass, because that makes play action work and/or creates doubt in a defense's mind.
“What fresh hell is this?”
"A man who picks a cat up by the tail learns something which he can learn in no other way." - Mark Twain