I'm a staunch believer that the best companies have the best leaders. The reality is that having bad managers can quietly cost a company millions. Their impact hides in attrition, disengagement and missed execution (think of that on a sales team). They can drive high performers away and create a terrible company brand that could take years to recover from. And let's not even think about bad managers who don't hold themselves accountable and ultimately become a liability to the company (i.e., litigation costs, scandals and discrimination claims).
Anyone who claims "leadership" isn't all that important hasn't had the breadth of experience to see what poor leadership can do to a company.