Euron has become one of the most powerful if not powerful characters

[DelroyStareyes]

As Littlefinger says knowledge is power...and I believe Euro has come into some very important information about the true nature of the supernatural powers or being in the world.I also think Aerons vision of him sitting on the iron throne with the corpses of the gods around him supports this as it means he knows for certain they are not real so he's killed them in a sense. This power tht Euron now has may be the reason he is so open handed as worldly things become inconsequentialwhen you have god like knowledge. He also sacrifices the priests to show that their gods are myths and won't protect them, or this may actually be a move to please the true power which he knows, if it's sentient that is, bringing a whole deeper meaning to the phrase " I am the godliest man ....."

[Whitering]

He may well learn about the sorcery is a sword without a hilt thing.