Thought It add this in. Since im doing mma, we do a lot of sparring of various flavors. I can tell you, the practicing your defenses against the air, and on the focus mits, are one thing, doing them against someone trying to hit you is way different. It took me, many sparring sessions before I could even beginner to effect my punch and striking defense in any meaningfull way. That for me proves that you need to actually be punched, in a serious way that involves some kind of pressure. That for me is a inescapable fact, you need to do your defense work not only in air drills, but with pressure, and with someone actually trying to hit you. I have seen it a bunch of times, like when a wtf Tkd bb competitor joined our gym. For me, ETinCTQX that is where your argument falls apart. This guy, was a good wtf black belt. Problem is, in sparriing, I was able to get inside, and it was over for him. He had no idea how to defend punches up close. IT would only take a few, before he turtled up and coach called the session. Sure if he can keep me at range he wins, but after a short while I learned how to deal with his long range tactics. So ya, my personal experience with it, is what is forming my opinions, as they are based in personal experience. I have said it before, but I find it odd my father is the only tkd I have met that can fight at range(his preference) and up close(were most of his SD fights took place) and can use his hands in meaningfull ways. Even his combat stance is different then most tkd stances I have seen.
I find that if you go on anecdotes, such as your experience with the black belt, everyone in every art has several that demonstrate their art's superiority or another art's inferiority. It just serves to reinforce my opinion that no art is better or worse, but that they all have their strong points and they all have practitioners of varying levels.
Incidentally, one of our black belts at the school where I trained had a friend who did MMA. I don't know what his level was, but he came to visit and train with us occasionally. He had a hard time fighting in the WTF rule set. After class we did some pick up matches and some of us sparred with him under a more open rule set. I enjoyed it. He was darned good, but I was able to adapt to him. But I've been practicing since the late seventies. On the other hand, one of our top guys in competition (he was a second dan with a total of three years in) had a lot of trouble with him. After a while, he adapted, but it was very challenging for him. It was a fun experience for all involved, but it definitely illustrated what a difference the environment makes.
A comment on the "WTF black belt:" You don't mention his actual grade (ildan, yidan, samdan, sadan, ohdan, etc.), so I am assuming that he is an ildan (first dan). A first dan in KKW/WTF taekwondo is essentially a novice. They've learned the beginning material. From first to second, they're honing their practice and instead of learning eight forms in twelve to twenty four months, they learn one and practice those that they've learned. They practice more than one type of sparring, the most recognizable being what is seen in the Olympics. Contrast that to a BJJ blackbelt, which takes many years to attain. Same color piece of cloth, but they represent very different amounts of time in their respective arts.
It takes a long time to develop a good taekwondoin. Other posters here, such as Twin Fist, who train in schools where a black belt is not awarded until two to three times longer (four to six years) essentially say the same thing; a year to two years is not enough to develop a strong fighter in taekwondo. It is enough to develop proficiency in the basics, which is what a KKW black belt represents, but not a strong fighter.
Training in an MMA, wrestling, or boxing gym will develop a strong fighter in far less time because that is essentially all that they're doing, while taekwondo encompasses a lot of elements in addition to fighting (forms, breaking, and sometimes there is a level of Korean culture, which varries from school to school). That isn't a value judgement; having more or less is not inherently better. It really depends on what you're tring to get out of the class.
If I was looking to be a strong competitive fighter quickly, particularly if I wanted a more handsy set of tournament rules, I would not enrole in a taekwondo school, at least not KKW. If I want to be a strong fighter and go to the Olympics, and specifically want to do taekwondo, I would be very choosy in where I train, finding the schools that do the best in tournaments, evaluating the level that the instructors may have reached in tournaments. Did they go to the Olympics? Are they local, regional, state, or national champions? Out of probably over two hundred schools in the DC metropolitan area, Maryland and Northern Virginia, there would only be a handful of schools that would meet that need. The rest are commercial schools that cater to kids and families.
On the other hand, if all I want is a class where I go in, get a good work out, mingle with people in a friendly environment, and maybe enjoy the activity with my kids, and have little to no interest in competitive fighting, a lot of taekwondo schools are available to meet that need.