Kyle,
I think that is similar to what I just typed on the Mandell book thread, but I won't type it again here, LOL.
I believe that perhaps the old Scots didn't have to worry about bunker depth on the seaside courses, they just took what was given, although this quote shows they did think a bit about it. When golf got to both inland Britain and then America and was built on gently rolling sites, then guys like CBM and Hugh Wilson had to think about how much fill to bring in and how deep to build a bunker rather than just carve one out of a dune. And not surprisingly, Hugh seems to come to the conclusion that a recoverable bunker has some merit to it.
The other takeaway is that golfers a century ago were also in the let's make it easier and more enjoyable mode, similar to today, while some surely were sticking to the "stick it to them" mode. 100 years later, there is probably still no consensus.
That said, nature does have it's say. If you route a hole over steeper ground, chances are the bunker is going to have to be a certain depth to fit the land, regardless of whether your theory of design says a fw bunker ought to be 4 foot deep or less, etc. And the beauty of that is, these kind of design rules are often meant to be broken. And, the designer has other options to compensate, i.e. wider fw, no hazards on other side, etc., when nature forces them to put a very deep hazard in a key place.
One thing Richard didn't mention on his bunkers on both sides example in the other thread is that there is nothing saying they have to be of the same depth on both sides. You can use the Eden principle on tee shots, too, i.e., the harder hazard in front, but if you overplay, you end up in more benign, but still hazardous bunkers on the other side. There is also staggering bunkers and other ways to avoid the straight "must hit it down the middle" non-strategy of a hole, or you might argue that the strategy of such a hole is to use your favored shot pattern to get the ball to a very narrow place. Or, if that fw is angled just a few degrees, consider using your opposite shot pattern to feather the ball into the narrow target zone.
So, Vive la variety.
Or as I used to tell clients, "Nothing wrong with a hard hole every once in a while!" (also, nothing wrong with an easy one, either)