> However, Ballmer was simply inarguably an effective CEO from the perspective of investors.
Reasonably effective, but not inarguably, since investor basically care only about one thing only: RoI. Under Ballmer's reign, the stock generally remained flat. Microsoft paid dividends, so investors still got some RoI, but not even close to what they could get on Apple in the same era.
Under Nadella the share prices went up by 50% (100% really if you count from when Ballmer announced he'd be leaving), so Nadella is inarguably a more effective CEO for short term investors by several orders of magnitude.
Nadella's strategy may be slightly more risky, so Ballmer might be an arguably better CEO for risk-averse long-term investors.
