You seem young. Like most young people you seem to have all the answers. You don't want to simply listen and do what is needed. Maybe you need to stop taking everything personal and do what is told. If he says "your side is wrong, fix it", how about you saying "YES SIR"! Then after that say please tell me what I am doing wrong SIR!
It takes two. So far with the attitude that you have shown here he may have given up on you.
So many come on here and express their side of things but there is always two sides to everything. I will never take what I hear at face value. And without seeing first hand and only getting one person says so, I can only try to read in between the lines.
I have only heard pure negative directed towards the teacher but nothing positive about what you do to make the situation better. That right there tells me something.
Your title says it all. "My instructor trains us to be tense/rigid". Unless the instructor said "I am going to teach you all to be tense and rigid", there is no way for you to know this, and it really make no sense. You cannot tell me other people’s thoughts.
You also say that he does not want anyone to get better than him. Again you are trying to tell me what someones thoughts are and you just can't do that. Most of my black belts at this point in my life are better than me. I can't stop that nor would anyone try to. I only can give the knowledge and it is up to that person to take it and progress or not. Only you can make yourself better or not.
The simple fact that your instructor told you that your side kick is wrong tells me that he is not trying to hamper you in any way. Now if you do the kick wrong and he says that was great keep doing it just like that, don't change a thing, well then I may think a bit different.
You need to look in the mirror and fist fix what you see in the mirror. You still have never told anyone what you rank is and that in itself raises concern. It has been asked multiple times. You create your profile with lies, for what reason no one knows but you. But you have already damaged your credibility because of this. If you lie about something so benign then what else will you lie about?
So because of all the things I have listed above you wll get no sympathy from me. I have 3 kids of my own, not to mention been teaching many many kids each day and I have learned to spot rather quickly someone that is simply looking for attention.