It's mind-blowing to me the number of people on these boards who take economist positions and just dismiss them because they don't want to believe that someone who studies economics for a living might know more about economics than they do. Worse than that, your response shows you didn't even understand his point since your critique is you don't think he grasps the idea of a hard-coded limit, and his point is exactly that the hard-coded limit is not absolute and can be changed. It's kind of implicit in his statement, but it's likely the hard cap limit will be changed because of future unforeseen problems with the diminishing block size. Regardless, his statement that investors "think they know but don't really know about bitcoin's supply curve" is accurate. However, if you're going to advocate that point you have to take the flip side with gold as well. We think we know the supply curve for gold, but future space mining could greatly alter the precious metals market in currently unforeseen ways.
I would also add one factor that can change the supply curve of gold and this is the modern philosopher's stone, I mean fairly cheap ways to get artificial gold 
Just the limit of 21 million is one of the chips of bitcoin and one of the pillars of its existence, thanks to which all modern investment strategies are built, and David Rosenberg unfortunately did not express any serious reasons why these fundamental principles should be violated, except for his fantasies about the protocol. 
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