I don't see where anyone is saying the "clerisy" class is responsible for the rise of the oligarchy. I believe the author is saying the "clerisy" facilitates the oligarchs in their efforts.

The premise as stated in the post is simply a description of what is obvious, the middle class is being eroded as the upper class is increasing it's holdings and control.

We can see on these boards how the "clerisy" works. We have a cluster of folks who are dupes, clerisy wannabees, who fervently embrace policies and practices which are dedicated to their own downfall. These are folks who advocate for the upper class to their own detriment. They are not the people who hire and fire, they simply approve of those who do.