Some pits are built different then others.
I’ve always been able to see my pups ribs, her mom is the same way, both super well fed but its just there body type, like some people are really skinny and some cant help but be chubby, same with dogs. I wouldnt worry about it, just make sure hes eatting and getting enough exercise and you should be good.
I give my pup breakfast, snacks inbetween, then dinner.
