So...this is just a screen cap from my website...obviously this is all just photoshop, but I based this off of @psacard 1952 Topps Mickey Mantle example on their website...which shows typical differences between grades.
Again, in my experience, dealing with DS shoes, I rarely EVER come across perfect 10's. Out of several thousand shoes graded, with deadstock, I'd say I'm running a rate of maybe 1 out of every 250 pairs that I'd consider to be perfect 10's, so that's basically a 0.4% perfect 10 rate. I get a handful of 9.5's, but most are in the 8.5-9 range for BRAND NEW DEADSTOCK shoes. And, even though we'd all like to complain about that figure, I don't know if it'd be all that different than graded cards...maybe someone can enlighten me?
Thing is, there are many different ways to look at flaws on sneakers. I would say it isn't as objective as card grading. Some people don't believe certain things should be included, others do. In your mind, if you can conceptualize the art and science of sneaker grading, what do you think the percentage SHOULD be?