That's assuming Steve's "editing" was alway right. We're not there so we don't know if there were good things Steve shot down and bad things he approved. And let's not forget that Steve initially faught porting iTunes to Windows, videos on iPods, an App Store for the iPhone, etc. In all those cases he has to be pushed and persuaded that it was the right idea. So this idea that Steve always new best is a fallacy. As far as Ive goes, there is now way he could become good in this role if he only has one foot in or didn't have total control. Now he has that control. And if he fails it's all in him and he has to take the fall for it. Cook gave him the responsibility, now he needs to own it.
Actually, that's part of what made Apple so successful. If an idea was so darned good that it survived such "editing" by Jobs, then it was practically guaranteed to be a success; in part because it was such a worthwhile idea, in part because those who thought it was a good idea kept after it, and in part because those who had the idea had to keep polishing and improving it to get Steve to accept it. If any old half-baked idea could get through, the resulting products will be half-baked, like Samsung phones.