This is what one report said of Casey (notice the part about "as other prospects"):
"Some scouts were disappointed Mittelstadt chose to use his draft year to finish his high-school career as opposed to playing in the USHL on a full-time basis. And Mittelstadt was unimpressive in the strength testing at the NHL combine, where he failed to do even one pull-up, completed just one bench press and recorded the worst VO2 max (aerobic capacity measurement) score of any prospect. At a shade under 6 feet tall but one pound shy of 200, fitness and conditioning do not appear, at this time, to be his forte.
"It's a testament to his skill, talent and potential he's still a top-five or top-six prospect," one scout said. "You can focus on what he isn't able to do because he hasn't trained as much [as other prospects] or you can easily imagine how much better he will be once he embraces strength and conditioning."
I definitely like his skill level and speed. And kudos for him for being strong (stubborn?) enough to make his own decisions, but there seems to be concerns as to why he didn't want it bad enough to compete with the other prospects. He seems to be the kind of guy that says, "if I think it's good enough, then it's good enough."