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.