My point is that language is not a requirement for humans to perform mental tasks absolutely. It is a fundamental requirement of a large language model.
That's a meaningless argument of definition. Replace the language input and output with something else and it's no longer termed an LLM. It's like saying that a "human who writes with right hand" fundamentally requires his right hand in order to write anything because without it he is no longer a "human who writes with right hand" despite that he is still writing (now with his left hand).