I think you are not giving enough credit to Cook. He trained under Jobs and is a world titan when it comes to supply chain. He is not some mumbo jumbo marketing/sales guy. Yes under his leadership Apple released some bad bets but he deliberately invested in a vision that Jobs created and spent years teaching him. This couldn't have been sustained post Jobs death unless Cook continued to instill the culture Jobs had created. Else you wouldn't attract the people needed to create marvels like their CPUs.

If someone else that wasn't directly trained by Jobs for years was hired, i'd argue that the culture would start to falter because one thing slides somewhere, then another, then another an soon enough 'A players' don't want to sacrifice their core years at a company that isn't instilling the values they want to work under. Cook himself almost went down that path with his budding career at Compaq. His family thought he was nuts to leave the growing company for Apple of all places. They didn't see the values that Cook saw in Jobs.