I’m sitting here eating brunch with my retired attorney DH and my son-in-law who is a judge. Their verdict? There is no such privilege. If an attorney did as Inigo-Montoya alleges and lied on filings they would at minimum be sanctioned and possibly be disbarred. (See: Rudy Giuliani). As DH said, attorneys work hard to become members of the bar and don’t want their ticket pulled.
Just supplying some corroborating facts. That is all.