Modern dietary science is quite different from it’s starting point. We know enough for soldiers, inmates, etc to eat exactly the food provided and be healthy. That’s the basic benchmark for success.

> it’s probably because it’s doing a better job.

Many birds are quite tasty, chicken however wasn’t part of our evolutionary environment. It also breaks down in the wider context, evolution would be adjusting things based on the overall diet and lifestyle of our ancestors which based on available evidence was quite different from our own.