Or people say "emotional intelligence (EI) is more important than intelligence," overlooking the qualifications in the EI literature that say that a baseline of intellectual competence must be met before EI can be a discriminating edge for leaders.
While EI and surrounding oneself with the smartest, most-competent people one can find are important--in fact, crucial--there is no getting around the fact that good leaders at high levels are typically very, very smart. The best leaders are not only smart, but they are intellectually curious and tenacious critical-thinkers
Elliott Jaques, one of my favorite management thinkers, wrote a lot about the requisite qualities of leadership. Jaques pointed out (rightly, I believe), that personality doesn't matter as long as the leader doesn't have significant behavioral shortcomings. Leaders come in all shapes and sizes and temperaments. I've worked with great leaders who were introverts and great leaders who were extroverts; I've worked with effective and ineffective leaders of all Enneagram types. But, argued Jaques, one of the qualities that a leader must have is cognitive power, or the innate mental ability to organize information, matched to the level of complexity of the entity he or she manages and ability to think in terms of the time horizon relevant to the role.
The CEO of a multibillion dollar global company with 100,000 employees must have greater cognitive power than the supervisor of six workers on the shop floor. The CEO has to manage tremendous complexity and think well into the future; the supervisor faces less complexity and needs to think through to the end of the day or the week.
If a manager is not intellectually matched to the complexity and time horizon of their role they will become bored (if they have too much cognitive power) or overwhelmed (if they don't have enough).
Yes, other factors matter. The leader must have emotional intelligence, appropriate values, a good work ethic, etc., but leaders who do not have the cognitive power to handle the complexity of their role will fail. Leaders with the cognitive power but who are not good critical thinkers will also fail, even if it takes them a little longer to do so. The worst leaders are the incurious and intellectually lazy, or even worse--dismissive of intelligence and learning. They will not only fail but do a lot of damage along the way.
Don't let anyone tell you that, for leaders, smart doesn't matter.
See "Executive Leadership: A Practical Guide to Managing Complexity" by Elliott Jaques and Stephen D. Clement.