The point of the children's book/Autobiography comparison is that there is a relationship between vocab and expressivity- not an absolute correlation where more words = more expressivity, because, like you say with the Hemingway example, that is always, even often not the case, but more a relationship of sufficiency, such that a general lack of vocab generally restricts expression, and below a certain point, there's very little you can do with it. The same principle applies to the Laffy Taffy vs Dead Presidents comparison. It's not an indication of the overall quality of the music, or even the quality of the lyricism, which is why I don't understand why people keep bringing up what trumps vocab and what is ultimately more valuable- it's just an indication of the breadth of the lyrics.
I should take an L for not clarifying that in the first post, though. I didn't mean to come off like Drake's complexity (which I would also argue is nonexistent, for different reasons) is disproved by having a small vocab. Only the grand pretentions about his literacy are.