I've always felt that CGC's dilemma regarded aesthetics versus technical grade. I once passed on some early Mystery Tales [Northland pedigree] because of severe browning to inner covers. I mean, they were baked. Another buyer, evidently more astute than I, had them graded, and they came back in the NM range - maybe 9.0 [it's a while ago so not entirely certain now]. I was shocked, but it is interesting to think on 'visible' versus 'invisible' faults after a book is CGC graded, and how various faults are treated. It's far more an art than a science, and art is opinion, which sometimes leads to discomfiture.
As for whether it is an 8.5 or a 9.0? I doubt very much it's inherent desirability [let's not say value] is much changed if the grade is lowered - the chip is still there, and so are the vibrant colors, and the exceptional structure.
I respect your opinion, but give me aesthetics any day!