Anyone who stayed on after the "extremely hardcore or quit" email shouldn't be surprised by impulsive and bad management.
I mean, of course we’d all like our engineering managers to be the technical variety, but we all know there are also the less technical “people people” managers in the pipeline.
An engineering manager without technical achievements has no authority
Have you ever read "turn the ship around"? It talks about how the captain of a nuclear submarine was able to turn leader-follower model into leader-leader because he had to rely on the judgement of his team.
Management is a different skill from engineering. I've met great EMs who never coded, but did have a great amount of skill in people management.