It seems like some people here forgot the main plot so I feel I should repeat it for them to remember.
MC is pretty much the reincarnation of a living god who dominated everything there was to know about magic but felt he had stopped progressing so he decided on ending his immortality only to be reborn with the right specs he desires. Of course he is going to be op, being a creature who knows everything about magic. As Gaia he was even unaware that he had long since ceased to be a human, he was fully immortal, far surpassed the limits of humanity, created hundreds of godly artifacts and the mere casting of a spell could cause an entire civilization to collapse as an after effect. That's how powerful he was. He keeps saying how people were stronger in his time, but even back in his time, his power was beyond anything other people would even come close to replicate.
The main thing about the story is the whole fact that the MC uttely lacks common sense, and how that lack of common sense changes the world around him.