Gates is smart. He is also very arrogant. But, he did not write the operating system that launched Microsoft.
So? Bill Gates did author a lot of other stuff that was brilliant enough in its own little world. Enough that there is not any excuse for him not being brilliant enough to foresee the Windows virus. Unless he was simply not normal.
You are right that he's not a coding wizard, but he was a hard-knuckled business genius. As I recall he wrote a very early simple BASIC --maybe he didn't do it himself. Why IBM gave Gates a monopoly on DOS seems a mystery--the old line IBM wouldn't have done that, but the skunk-works group who put together the original IBM PC was just trying to slap together something to compete with Apple and the other early micro makers, and weren't thinking too many steps into the future. Gates was. Gates had a lot of ego invested in MS-BASIC. I purchased the original 128 Macintosh computer, Apple had developed a very nice BASIC for it but Gates told Jobs that if Apple released it MicroSoft would not release any software for the Mac, so Macintosh BASIC never shipped. Instead I had a useless, worthless MS-BASIC interpreter. I was very pissed.