Gradually upsweeping flashed sand faces were common on golf courses in Britain and America that were sand/sandy loam (or light soil) sites before Merion East. No one is denying or questioning that and the photographic evidence of it is plentiful. Matter of fact, the original natural bunker formations on sandy linksland type sites were gradually upsweeping, as Wilson pointed out in his paragraph above, because they were created only by nature, not man.
When gradually upsweeping bunker faces created by earthen cavities first happened on compacted dirt (clay/loam) sites that had no natural sand is the question and I have not yet been able to find photographic examples of gradually upswept sand flashed faces that were essentially created by gradually upsweeping earthen cavities on clay/loam soils before Merion East. I'm not saying they didn't exist----just that I can't see any examples of them yet before particularly the fairway bunkers of Merion East.
Matter of fact, it appears on sandy sites such as NGLA and Pine Valley the original upswept sand faces were just the natural material of those sites and no sand needed to be imported for the sand floors of their bunker----definitely not the case with a clay/loam inland meadowland/farmland site like Merion.
There seems to be another irony here----eg if the sand faces on bunkers of sand and sandy/loam (light sandy soil) sites like a Pine Valley or NGLA got too vertical or perpindicular (which they occasionally did) they would collapse or slide thereby often necessitating maintenance fixes utilizing such things as railroad ties and sleepers or the breaking up of those sand upsweeps into smaller formalized bunkers with sod surrounding them or above them for stability. That kind of thing was clearly not necessary on compacted dirt clay/loam inland sites such as Merion----one could far more easily utilize trench-like bunkers (cop bunkers and such) on sites that had that kind of natural hard packed material. It was frankly no different on those compacted clay/loam sites than the rectangular earthen trenches in front of steeplechase berms!
But if someone does not see what difference clay/loam sites vs sand/sandy loam sites made to those men back then creating man-made architecture or which were which or why anyone today should care, that is just fine with me. I care because I think those men working with those vastly different materials and consequently vastly different types of sites back then to create various types of man-made architecture cared a whole lot because they had to---they were basically forced to care.
Was Hugh Wilson the first to create such gradual earthen upswept angles on the faces of particularly his fairway bunkers (before installing sand)? Maybe he was and maybe he wasn't but as yet I have not found any photographs or evidence of such gently upswept faces on any compacted soil (clay/loam) inland site before the fairway bunkers of Merion East.
We have a lot of courses mentioned in the post above. The first question is which of them had heavy compacted clay/loam soil like Merion AND which of them had such gradual upswept sand faces on their fairway bunkers (with no earthen/grass rampart above them) as Merion did? To answer the question of whether or not Merion was the first course this way both of those questions must be answered first.
If one goes back and reads Wilson's paragraph on bunkers posted in Post #3 one may find another contributing reason why he and Merion may've come up with this novel idea on hard-packed clay/loam sites (or even on sand sites that used railroad ties and sleepers)! It may've been driven by his (and particularly Richard Francis's) frustration with a particular aspect of the Rules of Golf----the very same Rules aspect with bunkers that interestingly still exists today (can anyone actually guess what that is?
). It may've had something important to do with the fact that Wilson figured out an interesting architectural way to deal with that frustrating Rules aspect and problem to do with bunkers, particularly fairway bunkers!
Again, if one carefully reads ALL of what he referred to on his unpublished paragraph (above) on bunkers it would certainly seem so.