If you feel like your grades define who you are, then the problem most likely isn't school but you. Never did I feel like my grades was part of me and, on the contrary, I've rather tried to calculate how much do I need to work to keep slacking at school/do something I feel more interested in.
Now, school systems often have issues, but blaming them isn't fair either for we are in an are of mass education and who says mass education says standardization/patterns. Hence, it's "adapted to most of people" in the sense that most of people can go through it and get to the learning goals.
What I mean here is that you can't ask from school to adapt to every one of us and to teach us individually following the best path possible for it's logistically impossible...
How bad school system wouldnt be, better go to school. Because how do You want to find good job or proffesion without education? You think someone will give You good job because You learned something from internet? How do You want to find place in good or even not so good university, if You don't go to school?
I don't know if this is true in Poland, but it seems very much what has been told to every millenials and it is very much of a fable. School/university gives no better job, at least in the West, than a """small""" diploma...
Hopefully, the dream still lives on in Poland, but in a country like France, this is absolutely not the case anymore and you are rather wasting your time to be unemployed/in burnout earning less money than some other jobs.
Plus education at school and universities don't teach your to be intellectually independent anymore for most of them... Which is kinda funny in supposed democracies.