Or if another CEO could have done better. While Microsoft was a mature company at the time, it's still part of a very high growth industry. He was CEO for 14 years, so just tripling the revenue (and that's in nominal terms, not counting inflation) isn't exactly spectacular.
Well, there's the CEOs of IBM, Sun, Yahoo, HP, DEC, Compaq, AOL, Palm Computing, and other formerly high flying competitors to compare against. I'm sure people could suggest a few others. Whatever else might be said about him, he didn't crater Microsoft while on the job.