Well the hairbow is not even Gaga's most iconic hair but okay.
Amy's hair is more iconic, especially because she never changed it. But it's more of a negative iconic since it was widely made fun of more than "OMG I WANT THAT HAIR" - kind of like Britney's shaved head.
But Amy's hair inspired Karl Lagerfeld's hair style for his Pre-Fall 2008 Chanel show.
And if you can inspire Karl to use your hairstyle in his show, that in itself proves how iconic it is.
I just don't get why people want to make sense of the world. At the end of the day, we are all living on some random rock in the middle of a big black darkness which we know nothing about. It is pretty much a lost cause. Don't agonise over it...just enjoy life!