It's been over a year and I see marked improvement in Shadow's eating behavior.
For example I've noticed he no longer growls while he eats. He no longer snarfs down his food in less than a minute. He no longer goes after Darwin's food immediately after finishing his. In fact, when Shadow finishes his meal, he leaves the kitchen like he has been taught to do. Instead of hanging around to intimidate Darwin.
This is progress.
However I've noticed other things. Shadow hates cat food with gravy. I guess the cat food manufacturers thought some foods would be more appealing if they had sauce. Shadow no like. I've caught him using his right paw to tease out the meat chunks and eat them, leaving the sauce behind. I would've never expected this from "Sir Greedy Gut".