Not really a lot to say here. I agree with almost all of what he says.
But there is one thing...
Differentiated monsters. What are the differences between a ghost, a shade, a wraith, and a host of other incorporeal undead that run around as transparent wisps? I want that defined and I want it to be clear when you see them in a line-up. Even if you don't know the names of the monsters, I want to make sure that you can tell that the creatures are different from each other—not just the same creature with a color shift and a new name.
I think that's the wrong solution to the problem. The problem is that D&D simply
has too many poorly-differentiated monsters. Rather than try to differentiate ghosts, shades, wraiths, and all the others in the host (and, for that matter, goblins, orcs, hobgoblins, bugbears, and all the other "low-level humanoid" monsters), surely it would be better to declare that these
are just the same creature with different names?
Perhaps even present these monsters as a sort of 'template-lite', where you get the base monster stats, plus a raft of customisable add-ons so that
this shade happens to be vulnerable to sunlight, or
that orc fights in a berzerker rage gaining a bonus to damage but losing out on AC.
Ultimately, we don't need thousands of monsters that are basically variations on a handful of basic themes - quickly cover the basics and provide us with the tools to go more specialised in these areas, and then spend your time generating
new monsters that aren't just a variation on a well-worn theme.
(And, yeah, I know that's not related to the art, as such. But it is related to the article, so...)