Ballmer doesn't strike me as an idiot and definitely not bland. He's one of the more colorful tech personalities. MS's almost unassailable lead in enterprise could be attributed to him and the pivot to cloud could not have happened without this. But he definitely fumbled hard on mobile (Windows Phone), Surface (IIRC the initial ARM laptop was a major flop and had a close to 1B+ writeoff) and the disaster that was the Nokia acquisition. I'd say he left at the right time, just as it was becoming clear that MS's bets on Windows Phone and hardware in general weren't paying off.
That's a pretty massive fumble. He was effectively trying to convert Microsoft into a hardware company; Satya marked the return to pure software, and Microsoft is now the biggest SaaS company in the world.
Rather than think of it as a pivot to hardware, I looked at it as MS trying to corner their share in the consumer market. Mobile and Social were the hot things back then and mobile threatened MS's dominance of the OS market. MS ultimately failed but they still owned the enterprise market and continue to keep their lead in desktop market share.
