I don't think Wiggins is too passive at all. If he looked it at times, it more of a function of Kansas' boring, swing the ball around the three point arc offense. After reading reports about him not being aggressive enough for the coaches' liking in preseason practices, I was expecting a passive player but he was aggressive right from the start. He is not one to shy away from shooting. One aspect of his game that he's going to show more is the ability to go coast to coast off the dribble. He was great at that in high school and there were times it looked like he wanted to jet off with the ball last season but then held back. He's going to be allowed to rush the ball up the court and attack.
Another thing false with his supposed timidity is that he didn't shy away from end of the game moments. In fact, he took most of Kansas' late game shots in close games and most of them were of him attacking the basket.
A player like Glenn Robinson III could be legitimately called passive on offense because he lacks the dribble drive game to force himself into his team's offense. That's not the case with Wiggins.
I agree with you that Wiggins is not as timid as he's being described. He appeared that way at times, but as you said it was mainly a result of Bill Self's offense. They would swing the ball around the perimeter while the defense played zone. Every time he touched the ball he would be out past the elbow with a defender on him and two bigs clogging the paint. His options were to take a step back 3 pointer or long two, blow by the defender (which he does with ease) and pull up for a mid range jumper (a low percentage shot), try to go through the two big guys who were waiting for him, or pass it back to the point guard. They never ran any screens for him or really any plays at all. Self is highly respected, but that offense didnt make sense for the talent he had especially when he was playing 3 or 4 freshmen at a time. It's a nuanced offense which requires jump shooters on the wings.
His jump shot isn't bad. He has a quick high release with good form which should improve. He shot 34% from three, so it's not like he struggled.
His handle is his biggest weakness, but it's not bad. He would turn the ball over a couple times a game when trying to force a drive through three defenders with a fourth defender collapsing on him. He would frequently try a spin move to get around defenders and that left the ball susceptible to getting swatted away. He needs to improve on that.
He thrived in the half court when the offense was broken up due to a long rebound or near steal. That's when he'd have space and freedom to make a play or drive to the hoop. Of course he was awesome in transition. His speed, athleticism, and body control are special. His second jump is incredible. His defense is also outstanding.
I have little doubt that he'll be a very good player, probably a perennial all star. The Grantland scouts are down on him, but there are many more that are very excited about him. There's a reason he was hyped up so much and still expected to be the top pick in a strong draft.