It is extremely doubtful (like 100% doubtful) that the flares are what is helping that horse. The article says they are self trimming. The fact is they are not trimming much at all, they are just flattening the wall that has grown beyond the sole to get it our of the way so the foot can balance itself.
Given the hoof history as described and how the hoof used to collapse on one side, I can assure you that what IS most likely helping is that when he was shod and lame the farrier was shoeing UNbalanced to the horse's own internal bone structure.
The collapsing foot was simply responding to uneven load and trying to balance itself. The soundness now has absolutely nothing to do with having flares.
Now that they are barefoot they have leveled themselves to their OWN individual internal structure so the horse is sound, The badly flared wall is supporting NOTHING . It just bent and got out of the way.
But the foot is now correctly balanced internally and is supported primarily by the frog, sole bars and heels.
So I guarantee if someone just started taking those those hideous feet forward on a post and removing the flare without changing the sole plane balance the horse could still be barefoot, be sound and have have decent looking feet as a bonus. I have done it myself many times on dozens of horses with feet just like that.