Nope, he screwed up even bigger than that. As recently 2005, IE's browser share was well into the 90's. Now, it's hovering roughly 40% depending on whose stats you trust. This on the desktop, to say nothing of mobile which would make the comparison between years even worse. This is after Microsoft recognized that the web was their big challenge, after the so called Tidal Wave memo.
He allowed IE6 to languish while the competition was growing.
To me, Ballmer is symbolic of Microsoft-with-ADD. They ignore things until they become urgent, and then shovel money into the furnace until victory comes. Look at Windows Phone - microsoft had a mobile offering when iOS came on the scene, but took years to move on with WP7. Desktops languished on IE6 for far, far too long.
And Vista's long death-march process and lackluster result is another point.