How about actual fighting?
I do not compete any more. I do, sadly, get involved in more physical conflicts than I'd like. A guy threw both a phone and a punch at me this weekend. The phone missed. The punch I moved inside of and blocked his upper arm; it hit, but with no power. He ended up on the floor repeatedly saying "ouch" and "I'm sorry" and "I didn't mean it."
What I did was effective. But I do not compete and have not for years. And what I did would not have been allowed under the rules of most striking art tournies anyway.
But I could still do it, quite effectively, against a man more fit than me and 30 years younger than me. Despite never having done it in competition.
I've done it countless times in forms. But we are told by those who don't understand forms that forms can't be useful.
I've done it many many times with cooperative and moderately resisting students during demos and teaching sessions. But we are told by those who don't understand these tools that demos and moderately resisting partners can't be useful.
Use whatever metric you like. But there are certainly plenty of people who are tired of being told that only ONE metric can possibly be used.
I can see how actual fighting could be considered a metric for evaluating the effectiveness of training. The issue I see with "actual fighting" as a truly useful metric, however, is that it's not a very good idea to endorse it for each of your trainees. What I mean is, if you do find yourself in a job where you have the opportunity to use these techniques as intended in real life altercations, you're lucky (or maybe unlucky... I don't know).
Point is, there is a distinction between what techniques are being learned and how they are being learned and tested. The question you raise isn't whether TKD CAN be effective. The question is how do we know whether you can use them, or that other guy, or that kid who just got his yellow belt, or that woman over there who has been training for 10 years? You are suggesting that real fights are a metric. I agree. Is it a useful metric? I don't know. I mean, yeah, IF you engage in enough fights. So, in your case, maybe so. But for most people? I don't agree that it's useful. If for no other reason that we (I presume) all agree that getting into fights is a bad idea. We actively discourage the test.
We also have to distinguish between what is being taught and what is being tested. There is a fundamental consistency in a competitive art between what you learn and what you test. In non-competitive arts, the link between the two is often tenuous. If I train in Judo and compete in a judo tournament, I am testing my ability to execute my techniques in the context in which they were intended. If I learn to box and compete in a boxing match, I am also testing my technique in context. Forms, drills, pad work, calisthenics and conditioning are all elements of my training, but in the end, it culminates in feedback and a consistent evaluation of skill.
In a non-competitive art, there is a huge gap between training and testing, which leads to posts like yours above, where the metric that you default to is actually getting into a fight. Which happens to be bad self defense. It's inconsistent. So you test other things. You test on execution of kata. You write essays. You focus on testing abstracts like character and respect. Perhaps you test on a clinical evaluation of technique or light contact sparring. I've seen a lot of belt testing over the years in a variety of arts, and I've not seen any testing that involves getting into real fights.