--Now, a posible problem with the story is that the mc is a Gary Stu, he is great at magic, at melee, with a bow, and on top of that he learns thing super easily. The only reason anyone is better than him at something is because he has not studied that particular thing for a long time.
Usually, if a character is good at magic, he is weaker at melee, so he needs someone to help him with that. Or if he is really strong, he is not that good with studies, making it so others can help him with the more intelectual tasks.
But the way you set him up, the only people that can beat him at anything, are the ones that have much more practice than him.
So now i think that your only option to balance him is probably to make a really big threat that his Gary Stu powers cant deal with alone... but if you do that, you will also need to make some characters also grow a lot in specific fields to be able to suport him meaningfully in the story.