Comments about my dog being too skinny… is my vet wrong?

My WGWL boy is 1yr old as of 12/13. His only known health issue is a pretty intense poultry allergy and a picky appetite. I keep getting comments from strangers and family along the lines of “why is he so skinny?” “Are you starving him?” I can feel his ribs but can only really see them when he arches his back (see pics 3&4). I can see his pelvis poking out a bit (see pics 1&3). Vet says it’s normal for his age & breed but I’m starting to consider increasing his feedings against the vet’s advice. I also could be exercising him too much? Thoughts?