Problem is he's too short to be a full time ruckman and on top of this he has a harder time finding possessions than Matthew Clark did. It's the same story as Sellar and McKernan, only he's shorter and makes them look like good key position players. Craig is destined to become a good SANFL ruck, but nothing more.
The issue with Craig is that he's only 195cm, but he's huge for a man that size. The guy is a behemoth. It's just too hard on his body for him to try to keep up with the athletic AFL players, and yet he's not big enough to out-tap other ruckmen.
Contrast him to someone like McKernan or Sellar, who effectively have normal-sized AFL bodies stretched out to 197cm.