Not all courses on Tour are the same. Some are just way tougher set ups than others. And really, it also depends on the strengths and weaknesses of the golfer. Errant driver equals bigger scores. Bad putter bigger scores. Bad iron play is easier to overcome unless terrible in the bunkers or short game.
I've shot 77 at St. Andrews from the tips. Was so-so windy. Shot 79 at Torrey Pines South from the near tips most holes. Not all. Shot 78 from the blues (not tips) at Congressional Blue. None had rough set up for a tour event. That would have made a difference.
Set up a course for a major, and the average 10 handicapper struggles to break 96.