Not sure that's accurate. The article suggests the "clerisy" operates largely outside the market system, e.g. doctors, lawyers, with the exception possibly being consultants. The PMC is very much a class in the market system.
The fact that a corporation has an exterior interface with the market doesn't change that most people in it don't deal with the market day-to-day. Even those who do form that interface are relatively insulated from it: a market analyst working to set prices still is evaluated by an internal bureaucracy, not the market itself. Only people in sales really end up exposed to the market because it's so easy to come up with a metric of their performance that's legible to the interior bureaucracy.
One of the reasons that teachers and doctors have such absurdly poor working conditions and pay (in the UK at least) relative to the value they bring to society, is that they're mostly paid via the state so the only way they can demonstrate their value is through striking. If the government takes a hard line of strikes and public spending then those industries suffer.
The term “clerisy” to me rings clearer than “professional middle class” as he latter ignores [edit: removed autocorrect nonsense word] very real distinctions between corporate lawyers and directors of NGOs.