Could Steve Jobs have been even more effective if he wasn't, in Spolsky's words, "a dictatorial, autocratic asshole who ruled by fiat and fear"?

It's possible. I know quite a few very talented ex-Apple engineers that left because they felt the environment was oppressive and stifling. Was Apple a better place without them?

I don't know. Jobs was crazy successful at what he did, but there's nothing in that to suggest that it was for the most visible reasons.