Last year we ran out Swider, Jimmy, Buddy and Girard with Edwards. No matter who wins starting roles this season, our athleticism will be increased. The new guys are all athletic and long for their positions. Most of them are wirey and not beefy, with long arms.
These guys, physically, are the prototype for effective defender in the zone. They'll probably suck for a while, as you and I know the rotations better than they do at this point. But they'll get better. Last year's team could practice for years, and they were never going to get quicker or longer limbed. The new kids will learn the system and their defensive abilities will be coming together right around the time we do our do not make the NCAA tournament.
I'm far more worried about our offense than the defense. The tools are there and JB is a master at coaching the zone.