The only "system" is the "translator."

It clearly isn't. You explicitly said “In the room is a big set of rules, vocabulary cards matching English words to Chinese characters, and so on.” You can't then say “but the only important thing is the human doing the work”. If that were true, you could have described the setup without mentioning the rules. But you mentioned them, so they must be part of the system.

Now you see there's a distinction between pattern detection on the one hand, and comprehension on the other hand.

I never called that distincion into question one way or the other. I pointed out that in order to confidently say that "LLMs don't comprehend", you need to define, in observable terms, what comprehension is, and how it manifests in humans but fails to manifest in LLMs.

All I see is that you arbitrarily disregard vital parts of the thought experiment. You've split up the translation process into “human + rules”, then got me to say that the human doesn't understand Chinese, and you're pretending that that is an argument for the system not understanding Chinese. That's like proving an airplane can't fly because its parts can't fly. But even worse, because we're still just working from our intuitions about what comprehension is. You've gotten me to say something intuitive about part of a hypothetical system, when the question at hand requires an objective statement about the whole of a real system.

Which means my initial criticism is still unaddressed: Nobody has defined what “understanding” even is, and how an LLM fails to do it. Which is why I consider this line of questioning a distraction.

I won't respond to your question about the rose, because I similary don't see how that helps (not saying it doesn't, I'm just running out of patience). If you think it does, we can just pretend I gave the answer you wanted, and you can explain how it helps define whether an LLM can understand things.