Your first 3 bullet points make sense, but this last one is where I think the normal theory behind "bullshit jobs" really falls apart. Every individual business has a large, strong economic incentive to not hire these bullshit jobs if they don't need to, so why should we think they would be so generous to engage in this "bullshit jobs charity"?
I think what is really happening is that as society advances, lots of rules, regulations and processes just build up and up over time, and this complexity eventually becomes self-sustaining, even if it greatly diverges from the original intent of the original rules.
Case in point (which is a common case I know) is the complete, total insanity of the US healthcare system, specifically how healthcare is paid for. Literally every single person I know that has ever gotten into some aspect of healthcare payments (potentially with an idea to improve the madness) eventually comes to the conclusion "The whole system is completely fucked, it should all just be torn down and greatly simplified." The problem, though, is now there are a ton of entrenched interests who depend on that complexity for their livelihood (I heard it referred to as "an abusive relationship" - Company A exists to "simplify some aspects of healthcare payments", which means they depend on the underlying complexity in the first place to exist), so there are no real incentives from the people that control the levers to simplify. So a lot of those bullshit jobs come about to manage that complexity, but it's not like some company thought "let's hire people to do busywork so they'll have employment."