Kibble isn't lethal, but grain free IS important.
Having said that, we did switch our B's from a good variety of kibble to fresh meat and bones/cartilage: where we live (Netherlands) there are several good brands of fresh meat in many varieties, and we supplement that with lamb ribs with meat, chicken, turkey and beef throats and the like, for additional nutrients and their chewing needs. From what I read it is a good practice to give about 5 different animals in a 2 week period, so they get everything they need. They also like vegetables (good fibers!) like cauliflower, broccoli, carrots, cucumber, cabbage. And a raw egg now and then.
Results: better coat, much less poop (about 40%) and much firmer. And possibly in the long run, less health problems.
Basically, it is no different from us humans: eat fresh (no processed foods), and eat what you were designed to eat - for dogs that is fresh meat (no matter what the kibble marketeers say). Strangely, many vets are against fresh meats.