Sorry, I didn't realize that gnomes had been brought up. I did see dwarves, and you answered that specific trumps general. Fair enough.
So, what specific element of gnome lore, in your view, allows for a gnome barbarian by the rules?
Umm, to be fair, most class' fluff is summed up in a couple of paragraphs. If we're going to talk about "so many pages", well, those pages are almost entirely mechanics and not flavor description. The barbarian (to stay with that example) takes up 5 pages of the PHB. 1/2 a page is a picture of a human barbarian and the other 1/2 page is the flavor text for the barbarian (plus a smidgeon on the next page). The next 4 pages are entirely mechanics.
Note, I agree that a "fluffless" RPG doesn't work. Fortunately, no one here is advocating that. After all, the knightly barbarian example above isn't "fluffless". It's full of flavor. Almost bursting at the seams. It just isn't following the flavor in the PHB.
Different flavor isn't "no flavor".