Although summer league is not the greatest showcase for big men, Zizic doesn't seem to pass the eye test. As I mentioned in the initial post, he has very little lift and lacks agility and mobility. He struggles to turn his hips over on switches and he seems to have heavy feet. His ability to switch on PnR and dealing with more athletic bigs (Lopez, Thompson etc) is not very promising.
On the bright side, he does have a nose for the ball and he has good fundamentals when it comes to "putting a body" on someone and boxing out, which seems to be rare these days. I feel like he would be decent if it were the early 90's.