We need to bear in mind that no dog food has been proven through peer reviewed studies to prevent or cause heart disease in dogs - the FDA states in their report that they believe the issue to be multifactorial. We also need to keep in mind that there are millions of dogs on this continent eating and thriving on all kinds of dog foods, including grain inclusive, grain free, raw and home cooked diets, so to insinuate that someone is putting their dog at risk by not feeding Purina or one of the Big 5 is really uncalled for.
There is no one dog food that works well for every dog, my dogs don't tolerate grain inclusive foods at all, and have been fed a grain free diet their whole lives, my oldest is a 12+ yr. old golden -recently vet checked and found to be healthy and doing fine, and was advised by my vet to continue to feed what he is doing well on, no need to change it. Bottom line we need to feed what ever food our dogs do thrive on, a food we are comfortable feeding, despite the fact that it may not be what the majority are feeding or what someone else thinks you should feed.
OP the only way to really know if a food is the right food for your dog is to give it a trial run and see how it works for him. Trust your gut, if you feel that NutriSource may be a better quality food for your pup than what you are currently feeding, there is no harm seeing if it will work for him.