But can an LLM come up with questions like what the definition of is is? Seems to me there's a lot of "depends on how you read it" type of stuff that lawyers excel at finding novel interpretations. So what coders thinking of as rules are much less straight forward to understand when it comes to laws

I think that’s a different task than the one OP is referring to. To your example, I’m not familiar with the capability of LLMs in that regard. I have struggled with using the AI features of westlaw when it comes to that sort of argument. (Basically, making an argument that strays from typical route, because that’s the position you happen to find yourself representing.)