There’s obviously a serious question about hermeneutics lurking in the discussion, but what I would like to see discussed is just what text of Mark is authoritative. We tend to assume that what we want is the most original text. What did Mark write?
But we count as scripture what was recognized by the church councils as scripture. (I ignore here whatever reasons they may have had for their choice.) The Gospel of Mary or the Gospel of Peter are not authoritative, but Mark is. What text of Mark were the church fathers looking at when they made it canonical? Does that matter?
I think it would relate (in a distant way) to the question of whether a gospel retains its authority if one thinks it was authored by someone other than the traditional one. If the church fathers canonized a gospel they believe to have been written by Mark, and then it turns out he didn’t write it, should their decision be reviewed?
I ask these questions because we often try to dodge doctrinal difficulties through textual criticism. I think that is not always (or often) the right approach. It has its value, but creates its own difficulties.
Worth thinking on, I think.