Hes clearly better than Middlestadt as of right now. Casey couldnt even put up a ppg in college whereas Pettersson broke the all time u20 record in the SHL. Theres no world where you can put Middlestadt over Pettersson as of now. You can say they are close, but Pettersson is surely ahead.
Mittlestadt wa amazing last year everywhere he played except college, maybe that was due to his college team being bad more than him being a bad player. He was number 1 prospect not in the NHL from world juniors till the draft. He was the only player on his college team doing anything and won the team MVP with .88 ppg as a freshman who couldnt even do a pullup playing against older and stronger competition.