I'm afraid I still didn't bring some of this home. IF we understand a protoGospel (UrMark?) to have been produced by a second/third generation Christian to flesh out and expound upon what previous Christians had left unsaid, in the same spirit of the birth narratives and infancy Gospels. Paul's silence (apart from a few interpolations) regarding any extended earthly stay and teaching of Christ, left a void that was filled by this new narration compiled almost entirely from OT typology and Homeric literature, set in the recent past under Romans. In many ways this resembles the Essenic methods of exegesis (I will not call it Midrash). Later recensions of this story continued to fill in the voids using the OT analogy and add a flavor of historicity (Luke's use of Josephus e.g.).
Mind you there was no one direction for these influences, for a famous example, what one writer felt was anti-Docetic (brothers) another later Catholic objected to.
In sum, there is no reason to object to the abundantly evident conclusion that Judas Iscariot is a literary creation. He plays a role entirely consistent with the method and objective of the writer, a method and objective continued by later redactors of the story.