Software Engineering leadership requires more of good soft skills than hard technical skills. I have had managers who were technically amazing but had weak soft skills, I had most difficult time working with these managers. Some other managers I had had excellent soft skills but weak technical skills, these managers were better at leading than those who lacked soft skills but still not the best because it was hard for them to grasp the technical engineering aspects that their teams were executing. Hence, its best for a leader to have both good engineering and soft skills but between the two its more important for a leader to have excellent soft skills. And the need for soft skills increases as leadership duties increase. For example, if you are managing a single team you will have time to still go over the code reviews and write some code but as you start to manage multiple teams you will not have time to get involved in deep technical details and thus your organization will be better served by your soft skills some of which I am discussing in the below articles. Please also have a look at the recommended books section for recommendation on leadership books.