For the which is heavier question, does it always pick the latter option?
It would be more remarkable if GPT-3 couldn't solve these types of questions. It might be another problem with the prompt design.
[1] Incidentally, the article is wrong in claiming that the state of the art before modern neural nets was Eliza. Rule-based chatbots got quite advanced in 2013-2016, although they admittedly were never capable of the sort of "true" understanding and long-term coherence that GPT-3 seems to display.