I'm sorry, as I stated most of my nutritional knowledge relates to pscittacines, which have different nutritional needs than chickens (unfortunately, as many pet bird foods are based on nutrition studies done on chickens). And while millet is not of little nutritional value, it is also in my mind a grain which is somehow (in my mind anyway) different from a seed. It also has a different nutritional value to a chicken, which eats seeds whole, than it would be to a parrot, which shells seeds before eating them, than it would to a human, which may use any number of parts of the seed. And chickens evolved in an environment where seeds would have been a significant portion of their diet for at least part of the year, so they probably are better able to use the nutrients in them than parrots.
But even for a chicken, I'm pretty sure that a diet comprised mainly of seeds would be unhealthy simply because they are high in fat. It may also be that we don't see the detrimental effects of seeds so much in poultry because of their shorter life spans. After all, if you're only going to feed the bird for 2-5 years max before processing them for stew...or even less than a year before processing them for meat...then the long term health problems caused by a diet high in fats isn't so much an issue. Whereas, in birds with a lifespan of well over 30 years (we have one
amazon parrot we see at work who is pushing 100 years old and is on the third generation of owners) who often get far less exercise than they were designed for liver disease, obesity, atherosclerosis, and vitamin A deficiency. And while some of these things are medical problems you would expect to see in very old birds, they are extremely common and play a big role in the mortality in young birds avian vets see on a regular basis.
Again, I'll be the first to admit that I'm not that knowledgeable in chicken nutrition. I know the basics, but certainly not enough to mix my own feed from scratch. And I think that seeds, including wild bird seed mixes, are fine as a treat. But they should be just that, a treat that is fed in moderation and not something that makes up a significant portion of the diet. Just like peanuts can be a healthy snack for people, but become an unhealthy part of the diet if you eat too much. And personally I like potato chips (and so far I think I've offered small amounts of potato chips to all of my pets), I just know better than to eat an entire 12oz bag every other day (although I probably could if I wasn't paying attention).