I disagree of course on the peripheral loading comment. An open shoe still packs with dirt like a bare hoof. And on hard surfaces it does not, like a bare hoof as well. Pads limit that function and horses benefit from a support material under the pad.
Yes, whether shod or bare, hooves *often* get packed with dirt. They often don't though & hooves on hard flat surfaces - whether shod or bare - are often left without support underneath. Because it's not reliable, and because dirt is unlikely to pack much into a foot like that and because it also may not provide enough protection to a sole like that on hard ground anyway, I don't feel it's really relevant in this situation anyway & the horse needs protection - I'd go for padded boots for now, if that suits him.
Agree that if talking flat pads with shoes, packing would also likely be helpful. Alternately, padding such as Vettec Sole Guard could be used without any other pad.