Being Junior World Champ doesn't mean a whole lot once the skater is in seniors. It's a nice credential to have (certainly better than not having it!), but skating history is full of former junior champs whose senior careers didn't turn out to be crazy medal-winning displays of dominance. Wikipedia has a list of all the medalists from all 37 Junior World Championships held so far. Of those 37 years of competition, only six JW champs have won senior Worlds: Fadeev, Petrenko, Eldredge, Yagudin, Plushenko, and Takahashi. (Kulik won JW and the Olympics, but never Worlds.) By the way, the only two-time winner of JWC is Adam Rippon, and, well. The best position for any guy to be in is to be his country's number one and then go out and destroy the rest of the field on the rink.