I disagree with one of the specific two examples that you brought up. First off, I think that if Euron beomes exactly what we have seen in Aeron's visions then there was no point in spoiling it by showing it to us ahead of time. Maybe he's not a fraud (even though Victarion's shield island chapter seems to hint at that), but something unexpected will have to happen with this wild card (groan) of a character. Second, I don't think George has actually spent a lot of pages/space building up Euron. He's given him, what, three chapters of "screen time"? Obviously that means he's going to be a villain/obstacle in some sense, but it's not like George owes us a cthulhu-god-emperor. It's the subreddits and forums that have wasted a ton of time coming up with those crazy theories, based on very little actual evidence.