Muay Thai is quite a torquing MA. MT emphasis is on power, and proper mechanism that allows the full flow of force. Which means, every kick, every punch and every elbow has the waist twisting motion with the joint that's hitting straight. Like hitting with a baseball bat. Although full force is created and very devastating, a miss will result in you spinning away from your opponent and facing your back against him.
The MT footwork is not fast-paced as the one in Kickboxing, and it's constant side-stepping. There is very little straight forward motion in MT, as people prefer to cover distance from the sides and by sidestepping you add MORE power into your kicks, punches and elbows [Hooks anyone?].
The kicks are very different from the one used in Kickboxing during Wallace's time. MT kicks has always been with the shin, from a sidestep with no snapping action. The ones used in Kickboxing has quite a lot of karate influence as Americans likes "safety first" as it is easier to recover from a snap kick.
Now what is kickboxing? Many say kickboxing evolved from MT but I doubt it. Kickboxing WAS mainly American boxing combined with the kicking techniques of Shotokan karate. Hence the flashy kicks and long range fighting preference.
The footwork in Kickboxing is fast-paced, jumpy and covers a lot of distance in a short time. Swaying, duck, weaving and bobbing is all used to get in and out, very different from MT. Kickboxers prefers to get in straight, not from the side by using slipping techniques such as evading a jab and then enter.
To be honest, kickboxers have better hand techniques than MT boxers. MT boxers uses only 4 techniques; Jab, Straight, swings and uppercut. Kickboxers utilizes almost all, from hooks, uppercuts, jab, straight, cross, shovel hooks, horizontal hooks and swings. The accuracy rate of a kickboxer is about 80%, while MT boxers are somewhere around 45%. This means that MT boxers have a harder time hitting with their punches as they are more used to kicking, and clinching whereas kickboxers are very skilled in in-fighting. MT boxers always resort to the clinch if they get near.
Kickboxers however have a hard time gauging their opponent unlike MT boxers. By utilizing the "teeb", MT boxers are able to keep opponent away from them to gain a breather, whereas a kickboxer's only gauge technique is the side-kick which shouldn't be thrown unless they know the opponent will attack. MT teeb can be thrown without the fear of "whiffing"[missing and then being punished].
Agility. Kickboxers have a lot more agility than a MT boxer. They are able to get in and out in a mere second and deliver their attack, whereas a MT boxer, you see him coming but you're unable to stop him. This leads to the question of who will endure the match longer? Well, if it's a fast paced match with only 3 1/2 minutes, kickboxers will have it easier, whereas if it's a prolonged match, it will naturally favor the MT boxer who enjoys defensive tactics.
Naturally, most Thai MT boxers are Sluggers. Most kickboxers are fighters, they enjoy rushing the match. That's why many enjoy watching kickboxing more than MT.
I hope that was sufficient information. If you want more, just drop me a line.
ps. . my comparison was between 80's MT and Kickboxing during the Wallace era, which I believe is during the 80's as well.