Catching and killing an animal does not make it any more aggressive neither. There are plenty of huntings dogs out there that will catch and hold prey while the handler finishes the job and this does not make them any more aggressive than your average pet.
For me personally, grains don't belong in a dog's diet, it is unecessary and only benefits the dog food companies to keep costs down.
These are the ingredients in Nutro Ultra
Three of the top five ingredients are rice in different forms and the reason for this is to keep the chicken meal at the top of the list making you think that chicken is the main ingredient which is not, rice is. Rice is rice, some are better than others but it's still rice and that is the main ingredient in the Ultra line and many other foods out there.