> it is not plausible that the Mahabharata as a whole is a record composed by a single author, at a point in history.

I agree. I don't think I argued against that? Responding to the wrong comment perhaps?

The Bhagavad Gita in particular is a section of the Mahabharata that has seen more revisions over time than the rest of th epic. In fact the name of the purported author "Vyasa" itself means "arranger", implying that he was organizing stories he received from others.