It's not yet clear why it struggles with arithmetic. It could be data-related, could be model-related, although scaling both seems to improve the situation.
In any case, GPT could still understand non-abstract things just fine. People with low IQ also struggle with abstract reasoning, and IQ tests place GPT-3 at around 83.
In any case, GPT could still understand non-abstract things just fine. People with low IQ also struggle with abstract reasoning, and IQ tests place GPT-3 at around 83.