And they are not weak. Nor are your intestines shorter, or your brain function different because your language has too many consonants. You can’t use these excuses as a general reason why your iaido is garbage, no matter who has told you that’s the reason.
Your iaido is garbage because you don’t practice, and if you do practice a lot, your iaido is garbage because your teachers are garbage.
Even if Japanese is such a difficult language that we need to have a special subset to teach foreigners, there are enough Japanese who are fluent in your language that they ought to be able to explain even the most subtle concepts. A concept that can’t be explained is one that either isn’t understood or is just a word without meaning. So you can’t use the excuse that concepts are beyond your comprehension, again, you just haven’t worked hard enough or your teacher is garbage.
Of course I may be wrong here, perhaps your iaido isn’t really garbage, perhaps your teacher isn’t either, maybe you’re being taught something that isn’t being tested, or maybe the person calling your iaido garbage has a different definition of garbage than yours, or your teacher’s.
On the other hand, if you are a big person with long legs your knees will be subject to a great deal more stress than if you are short and light. If your legs are heavily muscled, your calves and thighs may just meet a few inches away from your heels and butt which would tend to pry your knee joints apart, so you may be prone to injury. This isn’t a racial or a national difference, it’s a size difference and still doesn’t give you an excuse for bad technique.
Stop looking for excuses, pay attention to your teacher, take all other advice with a grain of salt and get to work. By the way, your soil and snow are not unique either.