Asking easy: does his stats higher than 7530(hardcore), 8160(charm), 6950(knowhow) and 64185 ego? Because it is his maxed stats, and if they are lower/equal than that, then there is no bug
If yes, answer is easy. if no, you should at least buy stats in shop and upgrade your equipment with legendary ones (droppable from Champions/Great Pachinko x10 +in shop section sometimes) that are your class or rainbow, or at least epic ones with thehighest stat for your class. Besides that, set a girl from your harem with highest stat of your class as alpha and second best as beta, third does not matter here as i know
And seriously, my lvl 100 side account can beat him, so please, tell me it is a bug =_=