So what I'm getting from the posts is that "skin and bones" isn't really something to worry about in a young puppy? ... but his ribs are visible.
How ribby are you talking about? If it's just seeing the outline of ribs, then the puppy is FAR from just skin and bones (if you can't see the outline of the last couple of sets of ribs, the dog is actually overweight or fat - this is a lean breed we're talking about, whose ribs should always be visible).
If, on the other hand, you're seeing prominent hip bones and the vertebrae of his spine as well - well, that
is closer to skin and bones, and the pup is underweight.
As youngsters, it is very common for pups to be a little bit underweight. As long as it's only a little bit (like being able to see all sets of ribs, not just the last 2-3 sets) then it's healthy (FAR more so than losing sight of those ribs altogether, which is an overweight boxer).
You're right that the food you're currently feeding isn't high quality. Generally it's best to stick with whatever the breeder was feeding for the first week, before making a gradual change. The canned food addition is also a good idea (but again, a higher quality version would be better).