Ancient Muay Thai is used in battlefield fighting, while modern Muay Thai is used in self-defense ring.
The difference between ancient Muay Thai and present Muay Thai is that
1, the boxing method of ancient Muay Thai was rough and straight boxing, while the boxing method of modern Muay Thai was introduced from boxing.
2. Ancient Muay Thai was dominated by routines, while modern Muay Thai focused on actual combat.
3. There is always a 108 style in the mouth of the ancient Thai boxing, with more moves and more gorgeous. Modern muay Thai omits those things and is easier to learn.
4. Modern Muay Thai is more reasonable and scientific in training methods.
I don't know the lethality of this move you said. I only know that it is generally not used unless there are special circumstances.
Each martial art has only a few practical moves, but it is not omnipotent.