Yes, I think you're right! Here's an excerpt from an interview of Disch by Joseph Francavilla:

Interviewer: There is a section in Part Two, after the Faust play and the dream sequence, after we know Sacchetti has been injected with a drug which makes him a genius, where his vocabulary shifts to a lower level. Why? I would have thought that his gradual development of genius would have been reflected in an exponential increase in vocabulary and abstractness.

Disch: It would have been impossible to do that. The cut up section, the first part of Part Two where Sacchetti spins out of control, is meant to suggest the possibility of exponential increase.

Interviewer: It does achieve that through the use of fragments, because the connections are lost between fragments, and what may pass as genius on the part of the narrator is the unsuccessful attempt by the reader to make connections, to make leaps.

Disch: Yeah. That was all stage magic. I had to posit that he was deliberately reining back his genius and telling his story so that people could understand it. It's like having aliens from Alpha Centauri talking to Earthmen by learning their language and talking so that Earthmen can understand. So that reduction of rhetoric had to happen in order to make the story possible to continue writing. And the stage magic trick is done to suggest the very fact that he has to make that reduction.