I too have a skinny, ribby boy that is 4 yo. on Pro Plan Sport who is the darned pickiest eater. I've tried everything and he'll never finish a bowl, always leaves some. I can get him looking pretty good at home but he always gets really skinny while at the trainers and daily training. I corresponded with Dr. Tim with the thought of feeding him Momentum just today and he agreed it would be better to try than Pursuit.
Ordered from Chewy today so I'll report back in a few weeks.
I also have a 6 mo. old Golden (not a picky eater) and asked him about Pursuit for that dog with the question of it's appropriateness for a dog that age in terms of calcium/phosphorous and a growing pup. He said the cal/phos ratios are absolutely appropriate for a 6mo pup so I may be making that switch soon too once she gets out of the yard.