Let me toss this out since the flow of the conversation has transitioned over the kicks and their usefulness for self defense. Okay, yes the legs are very strong. Yes, if you can connect with a well-placed kick it can work very well.
However...
I can only use myself, and those I've direct, first-hand knowledge of as a way to compare for the purposes of an example. Between the military and law enforcement I've been in uniform 28 years. I honestly don't know how many uses of force I've had in my career. If I had to take a ball park guess I'd say 700 - 800. Everything from knock-down-dragout fights to joint locks to throws to cavity pressing to etc. That isn't a boast and I'm not Superman nor am I bullet proof. I just work in a violent career, in violent areas for a really long time. I've verbally de-escalated far more altercations than I've been in and I'm proud of that. So no one think I'm trying to sound like billy badass. My point is that in all that time and all those altercations I've never kicked anyone...ever. I've only had maybe two people try to kick me with something akin to a straight kick. I can count on one hand the times I've seen a fellow Deputy or the bad guy try to kick each other. So kicks 'can' happen but just not as much as you'd think.
Many reasons for this; people of course in general aren't trained and/or comfortable kicking. But more often than not, the area of the altercation isn't conducive to kicking i.e there isn't enough room to kick. And remember, kicking in the dojang/dojo in the loose-fitting pajamas when you're warmed up and stretched out on a flat, level, dry surface in a venue that is well lite is quite a bit different than wearing normal clothing and shoes on different surfaces (which may be wet, slippery, sloping etc) and in dim light conditions. I just don't see kicking that often in real fights. Punching, grappling and improvised weapons are far more common.
Now I'm not saying it is a waste of time to learn kicking. Great conditioning and it 'could' be useful in the right circumstances. But we don't normally kick above knee height with an occasional waist height (not counting high kicks to stretch out). And we use only front kick (front and back leg), side kick and snap kick. That's it. Any type of high and/or refined and/or flashy and/or spinning kick in a real fight...well, I don't like your chances. As I mentioned elsewhere, convicts and inmates train each other on how do defeat typical TKD kicks. And it isn't hard, no offense intended.
And as a hard body conditioning martial artist, I'll go shin to shin with any TKD kicker. Unless they've conditioned their shins with bowling pins and tires again...I don't like their chances. That isn't a superman boast and shouldn't be taken as such, but those that do hard body conditioning will know what I'm talking about. Our idea of a BB test is four guys hitting and kicking you repeatedly while you do a kata. Anyway sorry for getting off on that tangent, the point is that kicking can be useful but I wouldn't spend but maybe 5-10% of my time practicing them. YMMV.