Well, that's my point (although you could say Xbox was an exception). Tim Cook is very well known quantity when it comes to execution, just like Jony Ive is when it comes to product design, but for innovation, we don't know how the team stacks up.
Minor quibble: the Xbox was started under Gates, not Ballmer. It was publicly announced 2 months after Gates stepped down as CEO.
I think this fits with your larger point however: Ballmer was not a product visionary.
Sharepoint. I'm pretty sure that's multi-billion dollar business for Microsoft.