“No True Scotsman”, eh? It’s as official as any other D&D product and had the standard D&D artists for the book (Jeff Dee, Roslof, etc.), plus some additional British (and well-known) artists as well.
The fact is, D&D art is all over the place with a lot of styles. People tend to remember the Easley, Elmore & Parkinson art, but forget some of the whimsy with Roslof, Jeff Dee and even Lockwood art (remember the halflings with the quill blown up in her face? Or Redgar using the half-orc’s face as a stepping stone to get to the top of a bluff?)
Yes, D&D art HAS changed, it’s always changing and will continue to change. But sometimes I think perhaps what chafes a lot of people may be the non-human heroes that show up more often, and it somehow rubs a group of folks the wrong way, as it gets away from the humanocentric view of D&D. Personally, I greatly enjoy the more fantastical takes that show D&D isn’t just our world with a bunch of people in quasi-medieval garb.