Stock market valuations measure future revenues. So if the reason is that the demand is so high that we are facing new bottlenecks, it doesn’t imply that the underlying capabilities are fake or that the demand is fake. Just that it’s another hurdle to cross.
I don't think many people are saying all AI demand is fake.
People are saying that there isn't as much demand for AI as is claimed by the frontier labs, which is pretty reasonable when you consider Anthropic has been floating the idea that their TAM is $30 trillion, approximately the entire US GDP.