Therefore the 5 highest rated slope numbers in the US at the tees you designated will be, under that system, the most difficult courses for an 18 handicap vs what a scratch golfer is expected to shoot.
The way you explain this is a bit confusing to me, so I'm going to restate slope the way I understand it.
Slope does not tell you how hard the course is for bogey golfers. (Bogey meaning someone with a 17 to 22 handicap.) i.e. we can't simply look at slope to learn which are the 5 hardest courses for bogey.
We have to also know the course rating. If two courses have the same slope, the one with the higher course rating is tougher for bogey golfers. At the same time, Course A with higher slope than Course B, may be easier for bogey golfers.
If you know slope and course rating, you can figure out Bogey Rating. That tells you how hard the course supposedly is for bogey golfers.
Of course, bogey and slop are just the raters' opinions. There is no guarantee of consistency in the ratings, from course to course, from area to area. I see lots of slope ratings that seem way off to me. In particular, the tough courses like Oakmont and ANGC from the tips should have much higher bogey ratings. Maybe the adjustments account for that.