I think we're superimposing narratives whatever way we see fit. We're not inside the company. I can see several possible explanations:
1) Stringer is the problem.
2) Stringer is not the problem: the executives that make up the board are the problem. In other words, systemic executive mismanagement. This is basically your suggestion.
3) The entire corporate philosophy is out of touch with the modern world. Sony is a company that has consistently specialized in superior A/V performance, and we're now in a world where very few people care about better image quality on their TVs, better graphics in their games, better sound quality in their music. Most of these industries are now driven by price, ease of use, and interface, areas where Sony is less strong.
4) Some combination of all the above.
I don't know which it is, but I can certainly imagine it is possible that a better CEO could come in and fix things. It's also entirely possible that Stringer is a very good exec, and that his competency is restrained by a stubborn, outdated company.