if you have to understand exactly what you're doing, why not just... do it?

That question completely misunderstands what AI is for. Why would I just do it when the AI did it for me in less time that I could myself and mechanically in a way that is arguably harder for a human to do? AI is surprisingly good at identifying all the edge cases.

i probably don't understand. the main thought i have re: llm coding is, why i would want to talk to a insipid, pandering chatbot instead of having fun writing code?

but, as an engineer, i have to say if it works for you and you're getting quality output, then go for it. it's just not for me.

It seems to me you're coming in with a negative preconceptions (e.g. "insipid, pandering chatbot"). What part about coding is fun for you? What part is boring? Keep the fun bits and take the boring bits and have the LLM do those.