Pérez Sanz is an up and coming 18-year-old, so might well be better than his ranking, whereas Josh seems to be playing at a level well below his ranking.
I half suspect that Josh long benefited from opponents going easy on him because he looked like he was 12 years old and that now he actually looks his age he has lost that advantage.
On a more serious note I do think he has over achieved a bit. He has a good attitude and makes opponents work for everything but he is a limited a player.