It's surprising how many C* level people don't use the software their company creates. I don't doubt that Cook uses an iPhone, but does he actually _use_ it, as in go off the happy path? And what about macOS? Based on past emails and stuff, Jobs was a decent "power user" of osx and a lot of bugs were fixed because he noticed it.
After seeing how Cook takes an iPhone out of his pocket, I'm not convinced he even uses an iPhone, or any smartphone for that matter.
If a company needs to rely on the CEO to file bug reports, it really shows their absolute lack of QA and testing along the way.
I don't think that's really the point of the CEO being a power user. Although Apple's software QA is definitely in question too.