That is the opinion of the writer on that site and while I may not agree 100%, my point is that their is more evidence for Mark wrting the original than there is for someone else and until the evidence is refuted by more subdtansial and concrete evidence to the contrary,all you have is conjecture.
You haven't provided any way to quatify why there is "more" evidence. There is just "tradition". That's not more. That's still just conjecture.