I feed all of my birds a mixture of game bird feed (designed for feeding pheasants and partridge for release) cat food, meal worms, a little cracked corn in winter, they also get whatever veggies we don't want. I have noticed in just one generation my birds have gotten leggier and more slim so I'll keep on breeding for that on top of working on making their nutrition the best I can find.
I think reckless breeding in general is destroying the peafowl hobby more than bad nutrition ever could but bad nutrition definitely plays its part.