The "Peter principle" rests on the assumption that organizations are rational meritocracies, and will reward people that are competent at their given task. And those organizations may (still) exist, but they are not the norm, at least not in my experience. I propose another, more important, principle as an explanation for the obvious incompetence of many managers: Competent people are a source of pain to higher level…
At the risk of seeming like an asshole: I think for every highly competent person who just lacks a bit of social graces and is unfairly punished by a defensive bureaucracy, I have encountered many more incompetent people who, due to Dunning-Kruger, don't recognize their own incompetence, and instead ascribe the rejection of their (mediocre) ideas to the unfair defensiveness of the bureaucracy above them. Or, in meme…
You are right of course, I am myself a living proof of that, and I would not wish it on my worst enemy organization to give me a promotion. That said, this doesn't really explain why so many incompetent people end up being promoted, which Peter (I believe correctly) documented. His theory is admittedly a bit more elaborate than mine, but it obviously builds on an endearing naïveté regarding the nature of organizations, especially large and mature such.