Domain specific LLM's absolutely exist, don't assume i've never seen one. You seem very misinformed on what is "literally not possible".

https://www.ibm.com/think/topics/domain-specific-llm

there are close to zero domain specific models that beat frontier SOTA models even in their own domain. (other than few edge cases like token extraction)

why do you think that's the case? lets start from here.

the real answer is that you get benefits from having data from many sources that add up expontentially for intelligence.

> LLMs are pattern matchers

but lets try to falsify this. can you come up with a prompt that clearly shows that LLM's can't reason?