I've played 7 of the 9 (not Oakmont or Kiawah). If just picking courses with name recognition, then the list is fine. Considering all the courses out there, then none of the ones listed make my top five if we're just considering difficulty. Heck, Nicklaus has designed five that are harder than anything on that list IMO (Old Corkscrew, The Concession, Idaho Club, Red Ledges, and Promontory).
I would tend to agree that Erin Hills is harder than Whistling Straits (or most of the others listed).
Winged Foot West, from the members tees with normal rough, isn't that hard compared to the others listed. Unless you hit it above the hole regularly ;-)