We criticize him for being old school because he teaches pitchers to a) sacrifice velocity for control and b) throw sinkers. Both of those are bad in today's game.
I don't understand messing with a guy with a ++ curveball. Giolito, with his current fastball and a curve is exactly what you want in today's pitcher. He has a 95 mph fastball that hitters have trouble picking up. Low fastballs get kilt, and sinkers/2 seamers have the highest BAA in aggregate of any pitch from 2016-present.