Some people have prepped months in advance to power level this class. Meaning they have all the necessary equipment, fully scrolled, fully cubed. The needed exp boosters. They have their Kishin/frenzy as well as their HS mules.
Also a handful of the people got a nice boost to lvl 120, by using the Pink bean potion reward that came with PB event. They saved it to see if it worked for Ark and it did.