"The ways engineers are terrible managers non-technical managers are often terrible too. In addition to that, they also know less about work itself and are more likely to be insecure about that."

I would put that as another human/personal trait, the ability to openly acknowledge ones limitations and delegate/defer when someone else has more expertise than you. For example, when making a technical decision, deferring to the tech lead & individual contributors.

If anything, a technical manager whose tech skills are/have slipped away is more likely to be insecure than someone non technical.