Yeah I don't get the hate for the whole maggie the frog section it doesn't diminish Cersei's character in my opinion.
It just feels cheap to take a character who was already believably written through three books, and to throw all that out and say that no, really all of her personality stems from her experiences with a mystical prophecy. Like, it feels like GRRM suddenly got nervous that Cersei's behavior was too over the top, and the sudden and violent loss of her son and her father wasn't enough to justify that, so he retconned in a bit of silliness to explain things that never needed explaining.