I see a lot of round kicks that honestly don't have that much power in them. A textbook karate/TKD round kick is not really an arm-breaker (at least not if you know how to block). But a muay-thai or kickboxing round kick can be. Those two really throw their hip into it and end up sacrificing defense and balance for power, where some other arts teach staying in control of your balance and defense. Similarly, the side kick I learned as a kid had almost no power in it, but when I learned a proper TKD side kick, that sucker is nasty.

FYI, I've managed a 6-board break with my side kick. That's about 1500lbs of force. I doubt a side kick using the technique I learned as a teenager would have gone through more than 2. They type of technique you use with a particular kick can affect its power a lot.

A lot of martial arts have the problem that they focus more on the art than the martial. As soon as you try to use it against someone who isn't respecting your rules of engagement, things fall apart. So against an opponent who only throws wild strikes, or who throws one thing at a time, Miyagi-Do would work very well. But if you tried to use it against a trained boxer, for example, you're toast.

For embracing the "martial" side of it, Cobra Kai (the art, not the show) gets that part right. In an actual fight, there are no rules of engagement. You do what works, even if it's a bit unsportsmanlike.