You CAN'T focus on *only* Mark, just as none of us can *only* focus on Matthew. ALL scripture must be used.
I disagree. He focuses only on Mark because it looks like it supports his presupposition. It is within scriptural bounds and proper exegesis to look at say Matthew 28:18-20 to show his error. Using the Mark 16 passage in no way negates Matthew 28:18-20 which he is trying to do. Not only is his use of that passage incorrect eisegesis but it does violence to scripture as it works to discount a portion of scripture altogether. In other words it appears he would rather just rip out the Matthew 28 passage. He presents them as if they are in conflict with each other. Of course this cannot be true so the onus is on him to show how he can take the Mark 16 passage and interpret it the way he does in light of Matthew 28.
He cannot do that so he avoids Matthew 28 like the plague.