the MCs game like power allows him to acquire every skill that has been used on him. In the beginning this is fine as he's learning things like beginner sword techniques and healing magic. This very quickly transitions to acquiring SS Level techniques that are given to him. With as much reasoning as "he seems like a nice dude" keep in mind these are serious clan secrets that aren't suppose to be taught. These are given to him by people who were complete strangers to him just a few days ago. In actuality I was completly fine with this as just acquiring this skill didn't make him op since he still had to train in it. Its everything that happens after.
My one real gripe that bothered me about the story is the extreme nationalism the author creates despite the situation seeming like it should have the opposite effect. The MC in the beginning is constantly talking about his love for his country it gets kind of nauseating after a while. It's made even more annoying when the story is on the galactic scale but he's still f**king talking about china.