I don't. Tim Cook is paid handsomely to be Apple's CEO. If Tim didn't think he could do the job, he could have declined.
Some people may gloss over Steve's bad traits, but he deserves the praise he gets. The Macintosh, NeXTstations, NeXTSTEP -> OS X, iPod, iTunes Store, iLife, iPhone, Macbook Air, Mac mini, iPad. I'm probably forgetting stuff, but those are all major innovations and successes for Steve (and teams).
The jury is still out on Tim. He's a great operations guy, shown some leadership in social issues Steve ignored, and has made some good executive decisions. But can he really drive innovation in the way Jobs did? Or I should instead ask, can Ive/Mansfield drive innovation the way Jobs did, because I think Cook wants to stay out of that and hope the golden boys can deliver the hits. Cook knows he's not a visionary and isn't trying to be. I think Cook has empowered the right people, and it's up to them to deliver.
I will say though that I don't think Cook is properly investing in Big Data to power Apple services the way that Google has been and will continue to. Apple has only historically dipped its toes in web services, usually to poor results (Mobile Me, iCloud). Maps was a big failure for Cook because it was a failure to understand the problem. Forstall was an easy scapegoat because Ive and Mansfield hated him anyway, but he was set up for failure to an extent because the data to drive a great Maps product wasn't there, and still isn't really there. This will continue to be the case as long as Apple thinks it can offer new services by simply packaging white-labelled data from 3rd parties with a pretty UI.