i agree with this. the reason why the muay thai fighters won is because they have had full contact hits since they were as young as six or even younger. But the kungfu fighters arent used to this. So while the kungfu fighters may have been more skilled technically they could hit a muay thai fighter a few times and not phase him, but 1 blow from the muay thai fighter could cause a knockout.
Explain to me how someone being able to take a hit is a testiment to the effectiveness of muay thai? A guy with no skill whatsoever can spend his life getting punched in the stomach and develop the stamina to take a punch. It doesn't mean his style is better, just that he has learned to ignore pain. Similarly, if some guy kicks a tree for a few years, he may develop insensitivity in his legs, but he's only going to be a badass for a few years until the strain on his legs puts him on crutches for the rest of his life.
The point is to avoid getting hit, or, understanding this is not always possible, to minimize the damage by deflecting strikes away from high impact zones. Someone's ability to take a punch does not measure an effectiveness in either.