I mean if AI output exceeds human quality then all humans will be redundant. So it would then be quite a brave new world!

My point is that I do not agree that LMM output will degrade all media (as there is always a demand for top quality content). So we either have bad LLM output and then people who care about quality avoiding such works. Or good LLM output and hopefully some form of post scarcity society (e.g., Iain Bank's Culture Novels).