I have encountered technical managers who were not good, for various reasons.
I think having a technical background is always a benefit, HOWEVER, it is neither necessary nor sufficient for being a good manager.
Management is weird in that understanding of the tech side of things doesn't correlate with influence.
It doesn't take a genius to know who is doing the work and who is looking for every excuse to be 'blocked'.
Managers simply know that they can't hire or fire and that calling someone on their bullshit would accomplish nothing, so they say nothing.
Managers are masters of soft power. Soft power is very hard for engineering/techie types to understand, which is why it works so well on them, because they don't even understand the game they're a part of :)
The fool is the person not understanding the game they're playing.
Techies who do other people's work are perpetuating the game they despise - they are indeed fools.
Middle managers who perpetuate the game are smart, because it is their job to perpetuate the game. It is not their job to change the rules of the game - that's the job of the techies who can refuse to 'pick up the slack', let targets fail repeatedly and signal to upper management that the game isn't working, forcing them to change the game, which the middle managers will once again perpetuate, because that is their job.
They just harassed some other person into doing it. He was a bit passive aggressive about it on some future calls: "Bob doesn't want to update the spreadsheet, so I will have Alice do it!" Anyway, nice guy, but didn't do any work at all, and he's gone now.
Most developers I know are good at human interactions, some even among the best.
I don't want to be put in that box, and I'm not willing to excuse someone bad at human interactions because they are technical.
Obviously some people are better at human interactions than others, and I'll be happy to adapt, but let's not imply causes.
There are also people who don't know how much they don't know.
They should not be making technology decisions or specifying how the work gets done. They should trust their reports to not bullshit (and if that trust is broken, those reports should be fired). I think having a technical background can be helpful for these managers, but I don't think it's strictly necessary, and they should be doing essentially zero technical work as a part of their management job.
I've found managers who are like this to be incredibly useful and productive, and a pleasure to work with. Managers who want to get involved in technical decisions just get in the way and cause problems. Unfortunately a lot of newly-promoted former engineers can't let go of the technical work.