Jesus H christ, you guys.
The penetration of the bag is also MUCH greater with the muay thai style, sorry for not explain myself more accurately to you nit picking asswipes.
Where the karate style makes a nice dent, the muay thai style kinks the entire bag and makes it bounce on the chain.
And its WHOLLY the result of the upper body mechanics of the muay thai kick, which you will never understand without dropping your preconceived notions.
I went through it myself as I described.
The Muay Thai style kick generates more velocity, more velocity = more force applied to the target. Making it significantly more powerful.
I've felt the difference being kicked in sparring, and it seemed a fairly significant difference to me.
The upper body mechanics, especially the torso twist/arm fling, which is very counter-intuitive to the mechanics and strategies employed by TKD and Karate stylists, is what makes the main difference.
If this is not good enough for you, go to a decent muay thai gym and see for yourself.
If anything, the karate style kick is more of a push, since it relies on muscular force rather than velocity to deliver force to the target.