Honestly, while I agree green size ought to be generally at the whim or discretion of the architect, if form follows function, whimsy in design ought not be the driving factor.....
It's a good question, though.
Yes, statistically, the par 5 has a short shot which old timers suggested meant a small green. Just because a few can bomb it home in one less than regulation doesn't IMHO mean you should enlarge the size. It should be harder than a long par 4 to reach, i.e, give a reward for a better than expected shot, not be figured as their right to reach a green just on distance....
There is also the "spreading out" factor Joe mentions. Taking the 99% of players who will play every day, you can expected approach shots to be from 20 to 200 yards on par 5 holes, so its much harder to design by any formula that way for every day play.
And, there is the maintenance end, where the supposedly larger percentage of short iron shots make more divots, if true, and the green should be larger. As with any short shot, sometimes a large, subdivided green makes some sense.
As with all greens, the micro climate has to figure in as well, with shady greens and lack of air movement suggesting a bigger green (or some tree clearing, if possible).
I vary my par 5 green sizes among small, medium and large on any course to try to create some noticeable variety, using all the parameters to select and design the size as best fits the site........