To get this straight right off the bat, this is not a thread for the purpose of bashing halter horses, simply a discussion of adequate weight bearing ability and the size of a horse's feet versus the size of their body.
What made me start thinking about this is when I bought some new shoes for my monster, Rafe. My first instinctual reaction was "Holy, cow. His feet are HUGE." Then I started to really think about it and came to a whole other conclusion.
I'm going to leave breed completely out of my part of this discussion because, frankly, I don't think breed should matter in this respect.
My guy is 16.2. On a light day, he probably weighs 1400 pounds. I consider him to have feet that are on the small side of normal for something his weight. He wears a size 3. I wish they were bigger but I didn't breed his parents and I can't change the size of hoof he grows or the size of body he carries.
Sorry, best pic I could find right off the bat.
Then I started thinking about all those horses who run around at that weight, or heavier, on a hoof that doesn't even get out of the zeros; 0, 00, 000, etc. Most people, especially if they don't have personal experience with seeing or handling hooves that small, they can't really fathom the size difference so I managed to find some other sizes up at the barn today and got a couple of pictures to compare.
You can see how small Rafe's feet really look when compared to his whole body, but can you imagine him with feet this much smaller? His shoe, the size 3, is the biggest of course. The other new one is a 0, the older one that's rusty is a 00. For consistency's sake, I searched to find 3 shoes made by the same company (which actually run about a half size bigger than most other brands).
Now try to imagine a horse his size, with a hoof that much smaller than what he's already got. How much more stress is being put on everything in that hoof from the tendons to the sole to the laminae and the walls, even down to the bones?
How long can a hoof under that much stress really continue to function?
This is his shoe with the 00 on top, just to better show the real size difference.