People like to look at the World Juniors because of the giant spotlight, but it's such a small sample size. Look at what Cozens and Mitts did in their D+1 seasons.
Mittelstadt had a very pedestrian 30pts in 34 games in the NCAA. The NHLe calculator I used translates this to 24pts in the NHL which is pretty much replacement level for a forward.
Cozens dominated the WHL with 85 points in 51 games in his D+1 year. The NHLe shows this to be 41pts which is without question a contributing F.
NHLe isn't perfect, but Mitts did not play well enough at Minnesota to justify moving on. The team was just gun shy leaving him simmer in the NCAA and risk losing as they did with Cal Petersen (and Jimmy Vesey).