Here's the thing: I'm not denying that you have failed or that you will continue to fail. All I'm saying is, it's not about something abstract and undefinable like /intelligence/ but a myriad of complex factors both environmental and psychological, that aren't easily quantifiable or even obvious.
You are not intellectually disabled, even if you're relatively unsuccessful at many things. The world is simply more complicated than a single abstract quantity being a complete life determinant. What does it take to get good at singing, programming, taekwondo etc. ? Training and learning in general is just a heuristic, some kind of probability that certain kinds of repetitions, reflections and examinations lead to insight and improve your performance. Whether someone experiences an a-ha moment and takes their skill to the next level is dependent on their previous learning history, whether the right connections get made, and you simply cannot compare two people's progress easily, even if you can quantify something like the amount of kicks performed because each kick was a different, unique experience. Instead of thinking that each kick somehow brings you to a higher level, try to think of each kick as a failed attempt by the person to figure out a solution to a particular problem through which a higher understanding is born. Skill progression is almost never linear, it's rather a continual staircase of plateaus and people can often get stuck on a certain level, even if initially they are talented and ahead of others.
The reason why I say "intelligence" is a cope, is because you're reducing all that complexity to a single variable, that you cannot even quantify or define. The world then seems much simpler: you failed because you lacked this magic thing and most importantly, there is nothing to be done. Why spend time trying to figure things out and gain a deeper understanding of a certain skill, when you can whine about being stuck or falling behind your peers because you were born with a lack of magical brain power thingy?
"Hey, if I'm not stupid, how come I failed at all these things, eh?" Figure it out, there's no easy answers like "intelligence". The difference between you and someone that succeeds is not talent or effort, but rather an actual understanding of why they were failing when they were. You are satisfied with "stupidity" as the answer for your failings. They ask themselves, why couldn't I block that move? Was I out of position? Was my stance wrong? Was I not paying enough attention? Was I watching my opponents arms instead of their feet? Figure out why you fail and fix it.
"Intelligence" is such a vague and useless concept, and I can guarantee that your estimation of your current capabilities is in no way objective, but rather just an emotionally biased perception of your own intellectual confidence - whether you can reasonably get away with calling yourself smart and whether others would describe you as such. Pseudo-scientific measurements like IQ are severely flawed from a statistical perspective and offer almost no predictive value except for extreme unintelligence, correlation being strongest for low IQ while anything above a 100 is fuzzier than random noise.
Long story short, the reasons why you fail are more complicated than lack of intelligence. Getting better at anything is rarely a linear journey from point A to B, but often a series of plateaus that last as long as they need to and always require gaining a deeper understanding of a problem. Training is a heuristic for finding a solution, not THE solution itself. If you fail to make progress after training for a long time, you don't put more effort into bashing your head against the wall, you change what you do.