Should I accept a promotion even if it means working for a poor manager?

BLUF: The head of another department asked me to provide more structure and organization to one of his underperforming teams. It turns out the team was underperforming because the manager didn’t manage his team. Now the department head wants me to manage the team, and report to the old manager (promote the old manager and keep him on board because he has domain knowledge). Should I accept a promotion even if it means working for a poor manager?

Six weeks ago the head of another department approached me and asked me to help them provide more organization and structure to one of his teams that was underperforming and had retention issues.

This came at a point in my career where I was looking to make a transition. In the ask, it was hinted that I could end up in a leadership position. I spent 2 days gathering info on the situation. The opportunity fit my strengths very well, so I agreed to help out.

Over the past 6 weeks, I’ve used relationship power to improve the situation. I have received positive feedback from all involved: the individual contributors, the manager of the underperforming team, and the department head.

It turns out that almost all of the problems in this area of the company result from a manager not managing. He is a skilled individual contributor, but he doesn’t manage his team. He doesn’t hold weekly staff meetings or O3s. His team doesn’t sit together. Retention is very poor, which leaves the team very young (0-3 years of professional experience). His directs were doing duplicate work, without anyone realizing it. He doesn’t manage their work, so directs get requests from all over the company. Directs feel overwhelmed because they don’t know who to listen to. He prefers working on his own projects compared to managing. This has slowed down his directs’ progress because sometimes they are waiting on him for decisions or guidance. But the manager reserves the right to make a decision or assign work when it relates to an area he is interested in.

The head of the department wants to restructure this area of the company. He is now proposing that we split the manager’s team in two. He wants me to manage one of the teams. But he wants me to report to the manager who doesn’t manage. I think the department head wants it this way because the manager has a lot of domain knowledge. I have the background to pick up the domain knowledge, but it would likely take ~6 months to learn it all.

I am concerned that, if I take the role, my new direct reports will go over my head to their old manager. Many of the directs are personal friends with the manager, and he will be able to more directly answer their technical questions. I am concerned that, in the case that a direct and I disagree, the old manager will side with the direct and not me.

I am also concerned that I would be managed by someone who has repeatedly told me that he doesn’t want to manage people. I am concerned that I will face a lot of the same issues that the direct reports face now.

I intend to express my concern to the department head. But I am not sure what else to do, or how to approach the situation.