The discussion you're linking to doesn't appear to discuss either general problems with the prototype paradigm or specific problems with adding properties/metho

The discussion you're linking to doesn't appear to discuss either general problems with the prototype paradigm or specific problems with adding properties/methods to the Date prototype. The closest it seems to come is a warning about not trying to modify the prototype of an object through its __proto__ property (or, I suppose, .getPrototypeOf), which isn't the same thing.