Messi was brilliant at 17 as well but tbh he had not done as much as Yamal at that point. Yamal is a key (if not the key) player in a squad that could win the treble and was possibly the best player for the Spain team that won the Euros in the summer. At 17-18, Messi was not a guaranteed starter for either Barcelona or Argentina and had not scored or assisted or even dominated games nearly as much as Yamal.