Ran,
Are we talking "member" play ? Or, Championship play ?
I would add an amendment to your query if I may.
If you're conducting a comparitive analysis, then I think you have to make the analysis based on both courses having the same green speeds, whether that be 10, 11, 12 or 13.
The same for the height of the rough.
One could also make the case that par should be the same, and others might make the case that the length should be the same for purposes of the comparison.
A good deal is based on the context in which the comparison is made, .... member play ? or Championship play
As you know, WFW converts the 9th and 16th holes into par 4's for championships while Oakmont converts their 9th to a par 4 for championships so that both courses are contested as par 70's, whereas, for member play, WFW is a par 72 and Oakmont a par 71
In my limited play of WFW, only two holes stand out as a rather short par 4, the 6th and the 11th.
While double and higher is easily attainable at # 6, it's a rather short hole for any level of golfer.
Oakmont has a series of short holes, starting with # 2.
# 5, # 7, # 11, # 14 and # 17 are also on the short side.
So from a member's tees perspective, I'd give the nod to WFW as the more difficult course.
On the Championship side, I think you'd have to examine the scoring histories, factoring in the variables in conditions, weather, etc., etc..
That's my theory and I'm sticking to it.