To be fair about what is or isn't enough to hard the axe and keep the demon inside how serious a grievance is is not up to us. what decides how bad a choice is for that is up to the god/s that were used to create it through the paladins/clerics. And since this is a game of d and d and not its own separate world to a greater extent it is up to the dm to determine what the god/s would think both good v evil and the level of strictness.
Plus while i know we are talking about fumbles and his pally levels, at least some of us are, he also has priest/cleric levels which is also holy. Well partial levels.
I know we can speculate and wonder and such but in the end since this is a comic based on another world that is fully controlled by a dungeon master then we have to accept the fact that while thunt may have logic behind everything that he does he also is treating it like a d and d game not purely its own world. Take the maze of many. I could picture the dm telling the players about the count up device to motivate/show them how hard this dungeon is.
So while some things may seem strict to us think about the world they are playing in so far. Think of the torture of the monsters that has been experienced. Think of kore being a pally even though he is how he is. This world is harsh and chaotic. You can't expect the gods (i guess the dungeon master is counted do to forgaths worship) to do things based on our level of logic. I mean kore only seemed to know about the axe after it went through him (if i remember correctly) which is something that gives its fully history to any paladin that comes in contact with it that does show that at least in the worlds/gods mind kore is a paladin and based on how the game works i believe means that at least by the standards of the god he worships he is good. The problem is we don't know what god he worships so we can't judge his actions based on the good vs evil in the same way as the one that gives him his holy powers does.
http://www.goblinscomic.org/08122007/
So based on the lore of the axe itself kore no matter his actions is a pally based on the rules of the god he worships at the least and verified by the dungeon master as such.
He knows the lore and history of it instantly.
The axe gains power from courage and valor. or if you prefer the demon is weakened by those things.
So we must conclude it is weakened by the opposite.
Big ears in the latest page says that he attacked kore from behind which is usually seen as the action of a coward. He is a verified pally from the rules of the world as not only did the weapon pass through kore but he learned about it instantly.
Big ears in a sense cheated the rules in order to cause harm to Kore. Something that is dirty and cowardly tactics depending on who you are talking to/with.
He attacked a pally even if it was kore as determined by the gods/dm and no matter our opinions is a fact.
Then when it finally broke it was when he attacked one of his friends. Not only that the only friend in the party who had levels (albiet partial) in pally as well. Also in cleric which were the two classes that took down the demon to seal it and are both considered holy. So he not only attacked one of his friends who has just started to recover from a huge torturous event, but also had levels in two holy classes.
While we might not agree with it it is up to the dm in the end to determine the gods actions and how severe the actions taken by the axe user are in terms of weakening it and or powering up the demon inside.
Sorry for the ramble but yeah.