Dr. Bowker is a research scientist but sometimes it only takes common sense to think about what is right and what is wrong.
Horses have hooves for a reason! They use their highly modified middle fingernail to gallop away from predators. The very shape of the coffin bone would tell anyone that the horse is not meant to bear weight directly on the edge of that sharp bone and certainly not if it is tipped forward with the bone column of the pastern straight up! I think on that we would all agree (except those farriers and vets who make money on that kind of pathology)
The leaf spring action of the joints of the foreleg combined with the incredible strength of the deep flexor tendon and it's attachments, is strong enough to hold a 17.3 hand horse (and his fat 200 lb rider) on one tiny foot as he lands from a jump! The integrity of the hoof capsule and it's design from the layers of horn down to the individual tubules are all responsible for absorbing shock.
But what most people don't even consider is the health of the laminar wall. It is the springs of the trampoline that hold the jumping surface to the frame. Without healthy laminar horn, the horse would HAVE to rely on a metal ring to keep the hoof tightly bound to the internal parts of the foot. And to be sure, if any blood and nerve function occurred, he would soon be unsound.
Dr. Bowker and others advise against periferal loading. The shoe is periferal loading but so also is a hoof that has over grown wall. Well .....here is where I believe we can look at the different wild horses which have adapted to various environments. The ferel horses from the wild west have very thick walls and soles, with a good amount of concavity and foot arch. The horn is worn into a functional natural hiking "shoe". The horses of the marsh lands around southern Spain have wide flat feet that help them keep from sinking into the mud. The wild asses and Zebras of Africa have very tight highly "contracted" feet to deal with harsh footing. Horses evolved AND adapted to various environments. But the hoof horn in a wild ass has a fat frog but no sole contact. That would be periferal loading as it is not loading the sole..
I do know that my horses very much like their feet when their coffin bone is well-suspended and they have an edge of horn slightly above the level of the sole. The ones of my herd that have unfortunately sustained laminitis from shoeing days and have a slightly ski-tipped coffin bone, do not have the luxury of growing a very high wall above the sole level. And the two horses I have that have very flat feet probably have flatter coffin bones as well. One was from being under-run and the other I believe occurred when he was born too early and his bones were very soft. Its a kindof a "so they're started, so they go" kind of thing. He is also genetically predisposed to having a wide foot as he is a warmblood.

Now the idea that bar grows sole. I can see how a researcher who is slicing sole samples to view under the microscope would come to that conclusion on many a horse. But the idea is like thinking that our fingernails grow the skin on our fingertips. It just doesn't make common sense. But in the case of my under-run horse, his bars do indeed mix with his sole horn. This however is a deformity, not a natural healthy condition.
And as far as those vets who believe the sole should be thick to protect the coffin bone, that is the case only if the coffin bone has already lost both it's concavity and its attachment. I know that wild horses can suffer laminitis from being trapped in a grassy area but then walk out of it if they are released. When we keep horses in pastures that are lush and have tons of acorns and are fed grain as well, we are causing the laminitis to occur. They can't walk out of it (unless the fence is down!) But think about this too. A camel walks on the thick pad of it's foot, with the toe nails in front. The pad is essentially like the horses' frog.