I spent nearly 3 years building up my strength, through quads and back. My thighs are 31inches. I have some muscular weight that helps travel through on a strong kick but the snap was better -10kg.
IMO, the best kickers in the world are some of the Thai guys who do little more than some plyo training.
You MUST understand the mechanics of the kick through repetition and knowledge of your own body.
No article, video or explanation can capture the understanding of the kick through practice. That especially goes for telling you what exercise to do.
My kick comes 90 percent from my hips and pushing from my calf. I've seen others who will use quad push off. So what are you going to do - follow somebody's exercise idea? I'm not convinced there is a one exercise fits all, short of bodyweight exercises and just bag work.
Good luck whatever you do.
Kru Yod has them lean legs. I don't THINK he squats 440lbs.