Tom Doak,
I think you have to create sub-categories of severe green styles.
You mentioned the 17th green at TOC, a green that I don't view as severe in terms of the putting surface.
# 1, # 3 and # 6 at NGLA would fit into one category with
# 7 at NGLA or # 17 at TOC in another category.
I can't see # 1 at NGLA at the end of a long to very long par 4
I can see # 7 at NGLA or # 17 at TOC at the end of almost any hole. The configuration of that green, internally and externally, works universally, from 360 degrees, from almost any yardage.
The configuration of # 1 at NGLA only works, in a practical sense, in a limited environment, a limited applicaton.
For the sake of MY discussion, I'd like to limit the context to clubs played by members or the public and not by PGA Tour Pros.
Severity, or the tolerance for severity lies within the membership. If, after adequate play, the green is deemed to severe, it will not survive intact. So, there has to be a balance between the challenge as manifested in the artistic talents of the architect and the playing requisites of the membership. When the two come into conflict, I know who wins and who loses, and sometimes it's the same or both parties.
An example might be as follows.
Had the 18th at Sebonack been a very long par 4 with a green that mirrored # 1 at NGLA, I think the criticism would have been ..... severe.
And, I don't think it would have been a hole of merit.
It would be viewed as a mutant rather than an enjoyable hole.
As a compromise, I believe the greens within green concept works best.
One look at # 3 and # 6 at NGLA proves that a severe green can present the challenge desired while retaining its playability for almost every level of golfer.
One asset of Sebonack that I forgot to add is the feeding nature of the terrain on some severe green sites.
This can be used as an advantage by the golfer if he understands them and if he can execute a reasonable shot that will qualify for use in feeding.