"If emotional intelligence is so important in leadership, then how do you explain the success of people like Jobs, Ballmer, Ellison, etc.?"
Great question. It's one that I frequently get asked when I deliver Emotional Intelligence trainings at companies.
One (somewhat dissatisfactory) answer is, "They were successful in spite of their disagreeableness, not because of it. Imagine how much more effective they could have been had they had more emotional/social intelligence."
While this seems true, it's hard to know for sure. It's conjecture.
To get into more of the science of it all, take a look at this interesting article from The Atlantic. It posits that 'disagreeableness' might land you either at the very top or very bottom of the effective leadership curve. Does this condone simply becoming really good at being a jerk?
I'm not convinced.