The key word there is 'impact'.
I don't think there's much doubt Jobs was a true visionary and made Apple what it is today, but as CEO running a big company, I really think Cook is a better manager.
He's take Apple from being a really good company with some excellent products and grown it something really quite remarkable.
I know he gets a load of schtick here because he doesn't reinvent the wheel each year but he's been a really excellent CEO. Hard to imagine anyone could have done better and certainly when Jobs died everyone thought the company would probably collapse not go from strength to strength.