I think it's fine to not disclose it. Like, don't you find "Sent from my iPhone" that iPhones automatically add to emails annoying? Technicalities like that don't bring anything to the conversation.

I think typically, the reason people are disclosing their usage of LLMs is that they want offload responsibility. To me it's important to see them taking responsibility for their words. You wouldn't blame Google for bad search results, would you? You can only blame the entity that you can actually influence.