I've done some Muai Thai on and off. From what I've learned from my Muai Thai training is they focus mostly on the low round kick. They do also work on front kicks mostly as a setup, punches, elbows, and knees but most of their training is on the low round kick and the clinch. When they throw knees usually they do it from the clinch and clinching and locking in Muai Thai is a whole field of study in and of itself, you could say its an art within an art. But aside from that the bulk of the training is the round kick, at least where I've trained. That is what I think makes Muai Thai so effective, they don't try to learn a hundred different kicks but rather focus on very few techniques with most of it on the round kick making the techniques that much more effective.