Most antiquities scholars think that the New Testament gospels are "mythologized history." In other words, based on the evidence available they think that around the start of the first century a controversial Jewish rabbi named Yeshua ben Yosef gathered a following and his life and teachings provide...
I don’t know that Mark having errors based on Old Testament prophecy necessarily means that the corrections in later gospels were fictionalizing a real event. That is one possibility. Another possibility is that the author of Mark wasn’t as well versed in Old Testament prophecy as the authors of later Gospels, who worked to correct this.
Yours is not a terrible hypothesis by any means, but I don’t think it’s as cut and dried as you think it is.
I mostly only read English so, wouldn’t any version I read have been translated twice?
It would have been translated once, directly from the Gnostic gospels that were found. But I’m not sure why that matters since they would be scholarly translations because they were found in the mid-20th century and the important thing is discovering what the Gnostics believed, meaning an accurate translation would be necessary.
I think you’re confusing the Gnostic gospels with something like the King James Bible. It’s totally different. We only knew what the Gnostics believed from secondary sources until the Gnostic gospels were discovered.