That particular vague sub-definition doesn't apply to comic book grading.
None of CGC, CBCS, PGX, Overstreet, etc etc etc have authority on grading. They all have different standards. None of them are authorities over your own opinion of a comic book's grades, for instance. CGC is a group of people comprised of individual "experts".
If there was a universally objective standard to appeal to, then I would concede that they have authority. However; No such thing exists. See: Getting a CGC 9.6, cracking it and re-sending it, resulting in a CGC 9.8.
Edited to add: CGC graders are authorities on CGC grading standards.