I think the majority of people believe Cook would do himself well by staying another year, and yes, it would likely help Iowa as well. But, I honestly don't see anyone thinking less of Cook because of his decision to leave.
This is just my opinion, but I really don't think another year at Iowa will make any difference in his prospects for professional basketball. He just doesn't have the skills to play in the NBA. He will play somewhere in Europe and maybe he'll end up with a year in the G-league but he simply can't do many things that well. Freak athlete, but doesn't seem to understand his limitations at all. He should never handle the ball except on the block, but that requires fighting for post position and having the footwork (Garza has good footwork on offense) to make a scoring move. Then in terms of rebounding position it is the same thing - he should lurk on the weak side, get position with his lower body, and get a ton of garbage putbacks (some of which could even be DUNKS!)