Look around at some other teams, there's freshmen D on other teams too. A top 4 that includes T Poolman, Ausmus, Wolanin, and Shaw is pretty dang solid if you ask me. Letting freshman play as a 5-6 dman is a best case scenario.
Imagine if (when) we lose T poolman, Ausmus, and Wolanin. That's thin considering Bast has played a handful of games over the past year and a half and Evers seems to be just a middle of the road college prospect at this point.