I suspect the point was to put enough personal context into the complaint to provoke sympathy, provoke noise, get it widely read and even hopefully get it across the CEO's desk at some point where the author's thesis will at least fleetingly get considered.
At that point, gathering information to test whether the temp system is a net loss or a net gain could begin.
Sympathy can lead to action, but provoking sympathy on an irrelevant point can lead to action you never expected. It might simply lead to finding the manager in question and dealing with that one problem. Whether thoughtful or emotional, focusing on the process itself would be more likely to inspire the prescribed changes.
I didn't get 'emotional', I thought the OA was actually quite measured and well written. The audience isn't Mr Bezos of course.
What I did get was annoyance at the lack of quality in the process. I agree that the author has not established that the lack of quality arose from the hiring policy. If the first manager had not been reassigned, would things have been better?