Since I got into golf by playing Medinah No. 3 as my very first round of golf (sneaking out on a Monday with my friend, whose father was a member) I know that the members in the 70's debated very hard on whether to host the '75 Open. They were against it, having tired of giving up their course even as part of the Western Open rota in existence then. Perhaps those and the '49 Snead Lost It Open were enough for that group of members, but times obviously change.
Matt, if you go back far enough, P2 changed its routing, grasses, etc. Overall, I would say both courses have about the same amount of changes throughout their history, but there is really no sense in arguing.
My sense is that the overall complaints about the current version of Medinah were that the greens still had to be kept wet and were not in top shape for the PGA two years ago. That was a direct result of NOT rebuilding all greens to USGA specs, but just doing 7 of them. I would think most in the biz, Rees included, would tell Medinah that ALL of the greens should have been rebuilt for consistency for major events.
There may still be a smaller problem in that I have seen 5 year old USGA greens play a lot differently than 1 year old USGA greens. I hope that on those other 7 greens, that they at least strip off the top few inches, add in the new sand and re-grass with the same seed. I think both members and players in big events would appreciate the consistency.