Hows it going?
I have to agree with Kathy, Bakers is flipping awful stuff (theres more E numbers in that than in a mcdonalds cheeseburger!!!)
I would expect a lot of your dogs thinness is due to this food, too much instant energy, not enough real nutrition.
Part of it is likely his age - he looks the same build as my own gsd x collie, who is basically not mature yet and when hes done growing up, he will grow out... slowly.
Part of it will be free feeding - thats extremely unnatural for a dog and they tend to pick out the bits they like, or save it for a rainy day (having food on tap not normal so the dog saves what he cant eat instantly, for when he is hungry but being a domestic pet he never IS hungry really.......)
It can be argued that no diet is natural, no diet we'd feed our dogs happily that is, and i would agree.
A wild or feral canids diet would be carrion, small rodents, birds, anything and everything he finds lying around, herbivore faeces, the odd bits of fruit and berries he finds.
I personally feel that a raw diet suits most dogs best and thats what i feed my four - its to my mind, the ideal naturally based diet for a dog, its what they would eat, if it was always available. Its what they are designed to thrive best on.
Sadly pet food manufacturers cash in on the fact that dogs are designed to SURVIVE on very little and will give you a shiny coat and bright eyes if fed sufficient oils and extra added cr*p, so the main content of the food can be cheap filler.
Great for their pockets, rubbish for our dogs!