And then he gets hit, again, with only 8HP remaining, from a creature 77 levels higher than he is. And we're supposed to believe he isn't instantly dead right here and now?
The poison right now has only displayed that it behaves like an acid, we have not seen any poisonous properties yet. Maybe if somewhere it was shown that it actually has debilitating and weakening effect, sure. But right now it's just a strong acid.
In fact, right now, the thing I'm wondering the most about is why did he even bother turning the knife into a poison knife if that element was completely meaningless in regards to this fight to begin with? It's like preparing a snare trap to fight a beast only to never use the snare trap and instead grab the rope and use it as a lasso right off the bat without even trying to lure the beast into the snare trap. Sure, you used the rope. But you didn't use it for what you prepared it for.
And why is the result of the eye stabbing a giant head explosion?
This is just meaningless gorey spectacle for the sake of it. I don't mind that sort of ultra gore blood splurting everywhere slop, but this is not what the story was suggesting this would be from both the start of this story and what appears to be the intent of the author with how this is trying to be framed as.
And his panic and fighting stance with that knife at the end is... also contradictory to the whole idea of a guy fighting with poison and his wits when he is literally still in the pool of acid-like poison that kept him safe from a creature literally tens of times higher leveled than these gobos. There should be no panic here, just absolute confidence especially with the details of his evolved skill.