I basically agree with your angle on questioning their calculations, though I’m not sure whether to defer to the authority of the writer, who is more or less a specialist and has more time to put in.
About whether he’d have done better investing elsewhere, he started with $400M from his father 40 years ago. Forbes argues that he’s now worth a bit more than 2B, which is about 5X. The Nasdaq grew 24X in that period. All Trump had to do was nothing and he’d have made much more money.