These are very astute observations and ones that I've seen as well after many years of work in tech. In a sense it's a case of "you get what you measure" where what we're trying to measure is how effective a manager is at deriving and delivering value from a team. However, a lot have found a way to "hack" how this value is communicated to their superiors.

A lot of poor managers I've worked with have a knack for taking work that is actually quite easy and communicating it as very challenging such that they (or their team) receive a lot of credit for it. As you stated in the other post, they may also be good at making their employees feel that there is great value in work that is also fairly trivial or non important. In a micro scale, this looks like a good thing (people are happy), but in a macro scale, it may not actually move the business forward very much.

At the end of the day, it often sadly boils down to "it's not what you did but what people think you did" that matters.