First of all we are talking around the issues. Even a deep bunker in America plays like a shallow one, because the sand is so perfectly groomed and because the green committee wants it to be fair and offer a chance of recovery ... whereas there are some sand areas at Pine Valley you could putt out of, if it weren't for all the footprints!
Melvyn is a proponent of "one size fits all" so I don't see the point of arguing with him about it ... that's his viewpoint on the subject, and he's entitled to it. I have to take a somewhat different view, cognizant of the fact that not every piece of golf terrain is suited to the types of bunkers he's used to in Scotland.
A shallow bunker is not necessarily without penalty, though. For greenside bunkers, a shallow bunker can provide plenty of difficulty if the edge contours and the contours of the green are working against you. I played Crystal Downs yesterday with a guest and we both saw some fiendishly difficult bunker shots from what Melvyn might dismiss as relatively benign bunkers, such as the back bunker on #1, the back right bunker on #3, the left greenside bunker on #13 [downhill lie in the sand, green sloping sharply away from you], and the right greenside bunker on #15.
Likewise, a shallow bunker forty or fifty yards from the putting surface is just as difficult (and arguably MORE difficult) than a deep bunker in the same location ... for the same reason that a stretch of short grass near the green is sometimes more difficult than if it were rough, because it gets you thinking too much about alternatives.
Fairway bunkers are a different story, as I posted earlier. There are three types: very shallow so you can reach the green if you can just strike the ball cleanly; deep enough that you're going to have to wedge out; or the in-between bunkers where you take a risk if you try for the green. I have built some of each, but I'm fondest of the last type.