I saw this thread yesterday but I was traveling and couldn't post a long response on my phone.
First of all, the quotes attributed to Brooks Koepka [originally related by me] have been truncated and taken out of context. It was a longer discussion than I could try to quote here, but his first point was that the revetted bunkers in the U.K. had real penalty value and had to be taken into account when plotting strategy, but that very few bunkers in America had that sort of impact on strategy for elite players, because the penalty for being in one was very marginal. Whereas, all the bunkers we build over here have a big impact on (a) the poorer player who struggles in bunkers and (b) the maintenance budget.
To Mark Kiely's point, some of the bunkers at Oak Hill did seem to be VERY penal and I 100% believe that Brooks would have identified those and played away from them or clearly past them or short of them, and would say that Hovland and Conners made major tactical blunders that cost them their chance to win. Indeed, he pretty much stepped on Hovland's neck about five seconds after he'd taken two shots to get out of the bunker.
Joe Hancock's point is a good one, that the value of a bunker is not just in the penalty for players who hit into it, but also the extra difficulty in recovery for the players who hit wide of it -- but that is a MUCH bigger factor for average players than for TOUR players who have so superior skill at stopping the ball on a little pitch.
Mike Malone's point is also a good one, that for visual and psychological reasons, the placement of bunkers will affect how the average golfer looks at the hole and plans to attack it, but that also has less impact on the pros. In my experience, fairway bunkers tend to lure players to hit toward them and past them -- which may be counterproductive in trying to keep those players from going low -- while greenside bunkers can be arranged to lure players away from the hole, instead of just firing at the flag.
I don't think fairway bunkers are useless, but I do think that their impact is overrated, unless you are talking about places with great bunkering like Ganton or Woodhall Spa or Merion or Royal Melbourne. From a designer's perspective, they are a crutch to use when the rest of your design is not so interesting. Perry Maxwell, in particular, hardly built any fairway bunkers on most of his courses [probably just because sand was scarce in Oklahoma], and I think his courses are very strategic . . . it's just that more of that strategy is based on the green contours, on trees and fairway shapes, and on the entrances to the greens. There are hardly any fairway bunkers on the back nine at Crystal Downs, and adding them would be superfluous.
Not sure if I've answered all of the questions directed at me, and maybe I've ignored one or two posts that were off topic or willful misrepresentations of what I've said.
Just to make things interesting, though, I will mention here that my plan is to incorporate deep and impactful fairway bunkering on the next two projects we are about to start, in south Florida and in northern Texas. Brooks' statement got me thinking that the important caveat was that it's pointless to build bunkers that aren't difficult, but it's not pointless to build bunkers that have real value. It just didn't make sense to try and make those bunkers at a tree-lined muni in Houston where they were trying to get 60,000 people around and not spend much on maintenance . . . the calculation is way different for two small-membership private clubs with ample budgets and [in Florida at least] few other natural hazards. I've contemplated using Ecobunker, but to start we are just going to try to incorporate some very skinny hazards with very steep faces, and then decide whether or not they need revetting . . . just as things evolved in Britain over a long period.