I'd say he was average at making money. It sounds impressive but you need to annualize and compare it to the market as a whole.

5.36B to 22B in 12 years = 11.7% annualized profit increase from 2012 to 2014.

However, MSFT stock appreciation was 22 -> 41 or 5.2% annualized. (Stock includes expectations of future growth, etc.)

Average S&P was ~7.8% for that time period.

Ballmer would have done better for investors by just investing in an index fund.