User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-121.54.32.168-20150720122914/@comment-109.121.37.127-20150720124211

It's not rushed. He fought against evil god Loki, True Longinus, Vanishing Dragon, Evil Dragons, etc. It's normal to get insanely powerful with those opponents + he is Heavenly dragon himself aswell True Dragon.