I think in the end, it's hard to separate technical leadership from human leadership. After you do your system design, you need to divy it up amongst the juniors to get it implemented. When deciding who gets what piece you have to consider what motivates them, what their strengths and weaknesses are, etc... But for sure your manager is helpful in figuring these things out.

At this level, your manager basically becomes your partner, with the same goal of getting the work done most effectively. Your domain is the technical, their's is the human, but there is ton of overlap in the middle