What you say is true and often quoted for both China and India. What is not often analysed is what the Chinese/Indian middle class want from a tourist destination.
From what I read domestic tourism in China and India is going strongly (prior to Trump's tariffs at least).
One thought that strikes me re Chinese tourism is that they have become used to an "internet environment" including payment systems that is completely Chinese. Perhaps Thailand needs to include that environment if it hasn't done so already.
Also there's the dreaded influencers who are enormous in shaping Chinese short term habits.
At the end of the day I think the wealthier tourist just wants to feel safe, comfortable and welcome