There might be two things going on here (your writing style is a bit odd if I'm truthful so it's quite hard to understand).
One is that you have a rubbish teacher, who is too heavy handed and dependent on this ridiculous system. I would make another appointment and ask why your child is getting so many strikes, and mentioning that they are becoming discouraged. I would be polite and 'let's all see what we can do to make school work for him' about it, but if really unhappy after that, I'd go to the headteacher and discuss the situation with them.
The other thing to think about is that by 9, children do become more introspective, thinking about their place in the world, more aware of competition, suffer existential angst (starts young!) and generally aren't always as upbeat and positive about life as they were say at 6 or 7 as they realise that that's not actually very realistic. Trying to maintain a smaller child's mindset of boundless optimism isn't possible either, and it may be that this is interacting with this new and not very good teacher at the same time. It can be hard for parents when children start expressing their negative feelings about themselves, or their surroundings, their experiences, when in the past, when they were little, they cheered up immediately if you put their favourite show on TV or whatever.
I don't think that means you need to put up with a rubbish teacher, if it was really bad you could think about moving the child but that comes with their own set of problems. However, your child is starting to think in more complex and sometimes more negative ways as part of their developmental process as well (sadly for us as parents!)- I hope you can get something resolved with the teacher. I'd also encourage out of school friendships and clubs (Scouts, sports) so that even if one part of his life isn't going so well, he feels successful in others.