This I can agree with. I just returned to the UK from a 3.5 month stint in Asia, mostly living in Bangkok and I can say I found a number of my day-to-day expenses were close to or sometimes more expensive than they are here in the UK, and the choice of imported foods (and domestic produce) is pretty poor (using Foodland, Tops etc.). Take a look at your next supermarket receipt or Food Panda/Grab receipt and compare to your home country's one and you may be surprised.
I earn good money and stay in a high-quality serviced apartment when I'm staying in BKK or wherever. It's certainly cheaper than something in London or Edinburgh but still, my 4* BKK residence was looking for £140/night during early February around Chinese New Year. Hardly "cheap".
I first came 20 years ago as a backpacker and have been back most years since, living there for some periods so have seen the changes in recent years. Obviously, exchange rates play a part but the £/baht rate has been depressed for some years now.
Where Thailand scores is on lower housing costs (lots of choices), eating local foods and not Western ones, jobs requiring manual labour etc. Not all of which benefit your average tourist vs someone living in the country.
Having said that, I was in Samui (Lamai) in February and March and both times it was as busy as I've seen since circa 2010.
During my Asia stay, I spent a week in mainland China (which isn't collapsing btw, it has problems for sure but the worst is probably over, though it has a looming demographic crisis still). A very good meal for 6 of us in a mall restaurant in Xi'An came in at £30 thereabouts. I paid way more in BKK for meals only approaching that quality. Other things are way cheaper so I'm not surprised some Chinese won't come. Thailand also has an image problem there as well, I was asked more than once if it was dangerous etc.
I also found Vietnam quite a bit cheaper but I still put Thailand comfortably ahead in the experience it offers tourists. Ha Long has to be one of the most overrated destinations in Asia ime.