You might not be hitting 100% with your foot, but you're pretty damn close to it. You wanna get in closer, and use your shin, not where your shin meets your foot.
Using your shin is like using a baseball bat. It's a lot stronger, and hurts a hell of a lot worse than a foot. Now of course, you're not always going to hit with your shin, and you'll hit with your foot from time to time, which is okay, but try not to make it a habit. You wanna practice hitting with your full shin, like in the Kaman video I posted.
Work on your pivot foot, it'll put a lot more power into your kicks if you learn to pivot well. Using your pivot is basically like using a whip. Your right leg is like the whip it's self where as your left leg is more like the handle of it. You really wanna use your hips as much as you can.
As for the Rutten video, I've tried his method and while it does work well, it's hard to do it effectively.