A manager and a project manager are different things. Usually PMs have no respect from me as a general sweeping statement. Often no idea how the subject matter works and don't do any actual work themselves.
But in the real world it's not feasible to have every manager come up directly through the workload they're managing. I am a test lab manager but it's a software test lab. I did the same role as my juniors albeit 5 years ago and was a developer in the middle. I understand the principles of their workload but not the specifics as our tools, the subject matter and our client balance have all changed in 5 years. It's my job to ensure they have what they need to do their work, and that the work gets delivered for our clients (internal and external). My role isn't "Test Engineer one level up", it's "Responsible for the productivity of several test engineers and the lab's output".
I could quite easily move to a different software test lab with an entirely different model (let's say automated software testing and verification Vs the manual TV integration testing we do). I could also move to a test lab for, say, electronics (my background) or radio technology, and still understand the field enough to do the job of managing the test lab.
If you can't trust your staff to do THEIR job properly, and enable them to do that, it's a concern. Managers are there to do exactly that, manage.
FWIW I was uncertain about moving into management and after a year, my doubts have been proven right. I don't enjoy the extra stress, I don't feel empowered to make enough change in my lab or to steer future growth. Line management isn't as rewarding as I hoped, largely because of having a small staff in a remote location. The energy and culture of our main office just isn't here. As such I'm very keen for my next change to be for less stress and less hours. I don't know if it's age, or stage of life after buying a house and getting married, but I've massively deprioritised work since taking this job on. Ideally I'd keep this income and go 4 days a week, and perhaps 3 days a week in some years. In reality I probably have to decide between more money (and hopefully working on the stress levels gradually), or stepping down to less money to go "back" to normal work. Not fussed in the short term as I just bring less and less of myself to work while I focus on home life.