Objectively, does Amazon pay it's authors fairly?

I hear a lot of people say they don't, but honestly I know people will always say they don't get paid enough for what they do. I've tried to find evidence that says one way or the other whether or not they are paid fairly and all I can find is people saying they deserve more but not pointing to anything other than their own opinion as evidence. Can anyone point to any evidence that they deserve more, something along the lines of "company *** pays *** percent more than what Amazon does and they are still a profitable and healthy company"