Mike,
Your notion of looking at a ratio consisting of the average score on a hole with the par makes no sense whatsoever. It is a misleading statistic skewed towards par 3s.
I disagree with you and Bobsy (surprised he agreed) with the general notion that par 3s are the hardest holes because there are fewer shots for recovery. The approach to the green on a par 3 is as preferred a lie as you like and when compared to uneven lies for approaches to par 4s and par 5s the difficulty is clearly with the non-par 3 holes.
Any given hole has a whole-number par while the average score for a field of scratch golfers is a non-whole number (lower or higher than the given whole number par). The most significant statistic is to look at is the average number of strokes or fraction of strokes over par if the assigned par is reasonable.
You can't even look at average strokes versus yardage as some holes are flat, some uphill and some downhill. Yardage in and of itself is not indicative of difficulty.
What was the average score on the 18th hole? If it was 4.44 or under, it would should be a par 4 not soley based on the statistic but also where it comes in the routing progression and the resulting psychological effect.
What was the average score for the 7th hole? Even if it were the approximately the same as the 18th (maybe it was lower) it should still be a par 5 because it is in the middle of the routing progression and it preceeds 3 difficult holes.
Then again, given the conditions courses in the "death zone" from here to Washington, DC, you have to factor out the green condition of the 16th in any degree of difficulty analysis. There was hardly and grass on the green and even a straight putt from 5 feet was an adventure.
One thing I noticed in a superficial look at the scores at Rolling Green was there were a few outliers (63 and 90) but most of the scoring was more over par than I thought given the soft conditions of a course playing around 6700 yards.