I think thinking that Grant can't be a star in this league is short sighted. I'm not saying he will be one, mind you, but the guy is oozing with talent and overflowing with heart and determination on the court.
He is a very athletic guy but not top notch. There are many guys who have other skills other than athleticism that make it. His shot is solid but not his 3pt shot. Hey, that is sort of normal.
He see's the court INCREDIBLY well. Guys are overlooking just how well he does that. When he gets the chance to drive, we will get to see just how well that is.
We don't really have a known #2 on this team so that is up for grabs. I wouldn't be shocked if KP or Grant eventually fall into that role. Lopez is gong to get a lot of touches, but probably is not going to be a go to guy on offense. Grant and Kp, can to a point, create their own shot. Grant can drive and usually pull up and KP can shoot over most guys. 
Hey, Pat Riley considered drafting the guy and Phil did, let's have some faith here...
The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift. Albert Einstein