Of the 52 courses played on the PGA Tour last year (including both setups at Chambers Bay), only 18 of them saw a four-day over-par field average.
In other words, most of the time, courses are setup to be played under par and the best golfers in the world are happy to accommodate.
Obviously, the majority of the most difficult courses are U.S. Open tracks, thanks to the diabolical work of Mike Davis. And in the couple of years when non-U.S. Open tracks were the toughest, such as 2011 when Rory McIlroy assaulted a rain-softened Congressional, the tour's toughest venues are still major courses.