Actually I think you are right. And I think that is where the confusion and myths appears.
There is no way to tell which ones are sinking them the furthest. It is what they do after sinking them that matters.
GRCH Rufus was a pressure biter. He did very little surface damage. Wherever he put his mouth would swell like a balloon.
In the beginning he was not considered a hard mouth dog until they started dropping under him. Even trhu violent shakes and re grips seldom did he leave surface damage to 'indicate mouth'.
An example. With your right arm grab your left wrist. Squeeze as hard as you can and while squeezing attempt to move your right hand up and down your left arm. The harder your squeeze, the better your grip, the least amount of travel. Basically only the skin on your left arm will move.
The slightly lessen your grip. Repeat. Your hand will slide some up and down your left arm.
Completely release the pressure and your right hand will slide up and down the arm freely.
Example 1 is a freak mouth dog. Imagine if there were nails in your hand sunk in. They would be deep, and with the tight grip the holes would remain close to the same size of the nail. The damage would be deep.
Example 2 the damage would be just about as deep, but the holes at the surface would be bigger. And to the eye more damage had been done.
The third example would be appear to be a horrific murder scene, the lacerations would be all over the arm, not all that deep but all over the arm. It would appear to be a lot of damage when in turn mostly skin wounds.
Lots of dogs accredited with hard mouth are really in group 3. it is the lack of mouth that appears to be a lot of mouth. (on the surface)
Mouth should be determined by the total effect not just the outwardly appearance.
I agree with your post.