A Simple Explanation of Why Your Manager is Mediocre
No manager wants to be a terrible boss. Yet even with the best of intentions, it's hard to avoid being moderately incompetent.
If I asked you to name a comedy about the workplace, you'd most likely name Officespace. In that classic movie, managers are the brunt of most jokes. The main character (Peter) stops caring about his job, and as a consequence is recognized as a future leader. Peter's boss drones on about paperwork, and is clearly not connecting with his employees. The popular Dilbert comic features a hilariously incompetent pointy-haired boss.
Your manager has a large impact on your happiness at work. They can impact your feelings of safety and security in your position. They can impact your independence and autonomy by micromanaging, or by not giving you the opportunities you need to grow. They can give too much direction, and at other times not enough. They can be disengaged, and unaware of the simplest details of your day to day work.
Overheard awhile ago..
Manager Alfredo - "What my engineers like is to be told exactly what to do. If they are told exactly what to do, they can relax and just execute on their instructions."
Manager Susan - "But these are pretty senior engineers, I think they get satisfaction from solving problems."
Manager Alfredo - "No, you don't understand, they'd prefer to be told what to do. It's easier that way for everyone."
I think many of your negative evaluations of your manager are likely to be true. They probably are missing details, coaching poorly, delegating ineffectively, and in general making a heck of a lot of mistakes.
I'd also argue that it should be completely expected.