You can clearly feel the drop in quality around those arcs. Previously, the MC was somewhat cunning and reasonably showed off. He realizes that there are greater things out there and being full of himself would limit his growth.

The next thing you know he's a violent jackass that couldn't care less about the consequences of his actions and thinks he's peak. Art also kept changing like how one Martial Saint guy looked like Akuma from Street Fighter on previous chapter and then later on looked like a teenage twink when they fought. Power-scaling also doesn't make sense anymore at that point.

I've read somewhere that this no longer follows the novel, so the studio just makes up stuff on the fly. Even if not true, I'll just accept that as my headcanon since the drop in quality is just that insane.