One of the reasons I switched to raw, was an unsettled feeling that giving the same dry food day in, day out must lead to some nutrition requirements not being met. I never felt that the problem was completely solved by changing and I add various bits of cooked human food such as quinoa, brown rice, well cooked veg, sometimes a few lentils or chick peas. The more I learn about pet and human nutrition, the more convinced I am that the best way to avoid deficiencies is to mix it up as much as possible. Of course this doesn't always work due to allergies or digestive issues but I have been lucky that my dog rarely has any adverse effects from her diet.
I have had issues with some complete foods leaving her hungry and making her go to the toilet excessively so I try not to mess with the main food without a reason but use one that has some variety anyway then I just vary what I add to it. I am still not convinced that I am getting it right although she seems happy and healthy.
It is hard to find a study on nutrition conducted without a possible bias.