It seems to me that your argument then winds up being, It has to be this way or else Christianity is wrong. Seems to me that you are risking quite a bit by hanging the whole of Christianity on not only martyrdom, but also martyrdom for very specific reasons.
Consider that you’re having to construct scenarios to support your logic. Reread your post. Now if there are Gnostic martyrs and Polytheistic martyrs, does your whole worldview crumble? Be careful on what you build your beliefs.
So given what you can find on this forum and the internet, do you believe it is proper to pass off the Gospels as being written by some of the first 12 Apostles?