In a remark below you state that it is.
Why are you contradicting yourself?
I am not contradicting myself. Your selective attention and liberal capitalization of part of my quote is the root cause of your misunderstanding. To your question,Shouldn't bunkers be functional, first and foremost ?
I said "Why can't they be both? If not, of course function should come first." You merely capitalized the last part of my quote and not the important distinction made by the "If not" part.Your reply was, "Because geometric architecture would seem to be more penal."
Why? Surface area? Because Raynor liked deep bunkers with steep grass faces? That might be true if other components of his bunkers did not subordinate the depth and the effect of modern equipment. Perfectly flat bunker floors offer a predictable challenge that was and remains a poor design feature due to the lack of variability as well as aesthetic and playability consequences. I asked you about this and you replied,Bunkers that rise from the low point in the bunker, toward the green, provide an intended assist in enabling the golfer to extricate himself from the bunker. I think that configuration inherently defeats the penal purpose of the bunker by providing a "cheat", an easier way out.
In addition, from a maintainance point of view, they're far easier to maintain. Keeping sand depth consistent, in bunkers that have sloped faces is very difficult, especially when wind and rain are prevalent.
There are hundreds of times more irregular bunkers than there are geometric bunkers. I think the maintenance issues have been addressed and managed quite well for the last 90 years.Balls tend to roll toward the green front of a bunker, and with bunkers that slope from the floor toward the green, the extrication shot is far easier. Golfers end up hitting off of an upslope, which is much easier than a flat bottomed bunker.
Steep vertical grass faces, depending upon the grassing, often hold balls and make recovery shots impossible, especially for seniors. Balls that hit into the steep slopes tend to come to rest near the base of the slope. Not only are the results predictable, but they are difficult to recover from. Shorter, or wider dispersion shots are not penalized nearly so much as the closer misses. Is that a good design philosophy in your mind?With bunkers with sloping faces, there's little if any impediment to advancing the ball. Flat bottomed bunkers provide more challenge, especially with steep faces.
You make one valid point about the upslope for many golfers, but that ignores the downslope and uneven lies in contoured bunker bottoms, which are far more difficult and overcome the easier upslope shot. Almost all golfers would rather have a flat stance despite the depth of the bunkers. You yourself mentioned the lob wedges, square grooves and balls that together compromise the depth factor. While it is intimidating, the easy stance and equipment overcome the apparent difficulty. I asked, Did Seth Raynor travel to Europe to study golf architecture? You replied,
"He didn't have to, he studied under the greatest architect of his time, one who had traveled to Europe to study."
It is arguable that Macdonald was the greatest architect of his time. I think the work in the Heathlands prior to and contemporary with Macdonald was more original. While many of these courses would be improved over time, Macdonald improved his course over time as well. What about Leed's earlier work at Myopia? Would you say this on par with Macdonald's at NGLA? Macdonald's idea to replicate hole concepts in America was fine in the early days of American golf architecture, but holding fast to that concept is sort of anti-American if you know what I mean. America likes to develop its own ways of doing things. The modern golf architecture that followed allowed the sport to move into an Americanization phase that proved a boon to golf. This is not to say that NGLA does not remain one of the world's great golf courses. It is far less geometric than the work of Raynor and Banks. They took Macdonald's approach to an extreme.I asked, What did he originate on his own that he didn't learn from Macdonald?
You replied, "Probably the same as Flynn with Hugh Wilson."
That is complete speculation on your part. What you fail to grasp is the design evolution and dedication to improved designs they made over time with foreseen improvements in golfers, balls and implements. Wilson and Flynn practiced an American form of golf architecture with shot testing, aerial demands on some holes and aerial and ground options on others. Flynn improved his designs over time. His accounting for wind improved over time. He learned to develop courses within a course with smaller subsets of holes that could be played if time was a factor to a golfer. He learned to make reversible courses. He learned economies in production, time management and cost accounting. He created a new model of design iterations done on paper and not on the ground. If not the first, he was one of the first to design accurately on paper and have the design translated exactly onto the ground. If you overlaid his drawings on old aerials and even many modern ones, you'll see they match up perfectly. He was an innovator constantly seeking to improve designs and techniques. He learned various perception techniques that got players thinking more, used far more offsets and angles to demand distance and line of play options and strategic demands. Wilson and Flynn devoted a lot of time to agronomic issues, working together to use new grass strains and planting techniques. Their contributions to golf extended well beyond design including fostering public golf in Philadelphia and the suburbs. Flynn also patented the basket golf standard, surely a better design than any golf standard Macdonald or Raynor designed 
I asked, "What is so daring about replication?"
You replied, "Do you see any meaningful replication today, or over the last few decades ? If not, that should answer your question"
Is that the only conclusion you can draw from the evidence?