I think he did need help because the upper 10 demon summoned clones that can use the 6th fang. Back then, he only had the incomplete version of the 7th fang that could not completely defeat the demon who used the 6th. He was simply outnumbered, and his skills aren't great at AOE attacks.

As for edgy, I get what you mean now. You are using it ironically versus the original meaning of "bold, provocative, avant-garde." I can see why you would say that, but I do agree that in this story it isn't annoyingly glaring. I think the reason is because the entire world is dark and grim. For example, I wouldn't say Bloodborne is edgy, but Arifureta definitely is. When only certain characters behave and look unnaturally different compared to the rest of the world, they seem extra edgy.