I dont think the course is unrealistic at all, as a matter of fact I think that WGT actually nailed the Oakmont setup to rival what it would be like under intense US Open conditions.
The main fundmamental difference is the ability to work the ball left to right. The greens are so fast and with undulations galore, so not being able to work the ball against the slope is the biggest reason I see in not being able to hit and hold greens. That is probably worth at least 2-3 strokes for the field, and considering there is a pool of thousands players here Vs a couple hundred, its not horrible to think the cut would be a couple strokes less.
I also think that many people here underestimate what it actually takes to be "great" at this game. I am a master, but NO WHERE close to the top players, and I know it is due to the amount of time I spend studying what it is that I am actually doing wrong when I play. I dont think being able to drive the ball more than 250+ is a deal breaker here because when it really comes down to it, it is up to who is going to get up and down from 40 yards in and who can make the tough breaking 5-8 footers. Playing Bethpage last year I thought the same thing, but eventually I realized that course management was a bigger factor than just distance and spin.