Not true at all, Muay Thai is Kryptonite to western boxing & far more effective at ensuring a boxer is ineffective. Knee counters to punches as well as brutal low kicks to the heavily weighted lead leg are the two obvious examples.
Competitive sport Muay Thai is actually mixed with western boxing, and pure muay boran disapeared from the rings since the introduction of boxing type training and techniques. guess why...
Same with karatekas in K-1, you dont see tsukis, uraken punches or wing chun guys.