Was the genius or dumb person really born with different levels of learning ability, or were they just raised differently: nature vs nurture ?
The "intelligence" of one species vs another comes down to differences in cognitive architecture, ultimately reflected in ability to learn and predict/infer. Intelligence, as a capability, not IQ test score, is best regarded as ability to learn from experience and use that learning to accurately predict future outcomes, ranging from passive observation, to the outcome of one's own actions, to the ability to reason.
Comparing the intelligence (not knowledge) of different AI system to humans should therefore be assessed by comparing their ability to learn and use what they have learnt.
An LLM is what it is - a language model, not a learning system. It's really an expert system of sorts, highly capable in terms of what it can infer based on the knowledge it encodes, but with very limited ability to learn.
When you talk of comparing AI to a genius/professional/graduate/etc, you are really talking about comparing level of knowledge, comparing one expert system to another, which is fine and perhaps useful in some contexts, but it is not the same as comparing actual intelligence - learning ability, and especially so if you want to discuss general intelligence which is all about the ability to successfully take on any task (perhaps needing to learn it first), not just do well on some limited set of tasks you are already familiar with.
If ability to learn is limited to one modality, such as language, then that indicates a lack of generality. A good test for whether an AI system is in the same ballpark as a human in learning ability, aka intelligence, would be whether it can (at run-time) learn language itself, from a blank slate start, when running in a suitable environment.