Pat,
Any sloped bunker will wash sand away, especially if overland water comes over the top. Herringbone drain tiles near the top, and the new fabrics help a bunch, but gravity isn't just a good idea, it's the law, and sand will wash down if the rain is hard enough.....
I tend to do flatter sand bunkers in rainier - and windier - climates, but have even seen flat sand bunkers wash in a big enough rain. Its the same amount of water coming down whether coming down a grass or sand slope! I got a call today from my new course in Minnesota, where the new sod has washed down the banks in a few big rains, so washing sand is not the only problem, either.
Here in Dallas, I find that if only the edges of the bunkers flare up steeply, and the base of the bunker is in the 10-15% range, they will withstand most rains, and wash out about 3 times per year. This, along with consideration of mechanical trap rakes, tends to make bunkers bigger in scale, and more "non golden age like" if you will, but it is a compromise made after years of experience.
All bunker design is a bit of a compromise, really. If the Owner wants the "MacKenzie look" then the super needs to plug in about five unscheduled "sand shovelling days" annually to get that look. Flat bunkers have visibility problems, and in my mind, are not as attractive a feature, in most cases.
So is damage representative of flawed design? Not IMHO. Rather, it is a conscious decision of what maintenance problems to give a super versus the look an architect wants. That decision should be different, likely, for almost every course to best fit its goals.