Respectfully, you are changing the point. His "marketing ploy" is to portray this as true. To then hide behind "but it's fiction" is spurious - both on his part and on Ron Howard's.
As did many 18th and 19th century novelists like Horace Walpole and Wilkie Collins...to the point where their novels were framed with epistolary evidence from the alleged parties ‘involved’. No one took them seriously either. Or rather they took them at their worth as novelists. I think the key difference between us is that I look at this with literary/historical context in tow.