The question is asking about myth, and for that, I would say no, it is not a myth but where is the proof? Correct?
I think it is not that easy to find someone who do forex trading as living apart from wonderful members in such forums, but most of the time, traders easily give up or failed because of no proper sound plans were made entering into forex world.
I don't think it is a myth.
There are many traders who are successfully trading forex for a living. It is not about what you do, but how you do it. If proper knowledge is gained and one works on risk management and planning, forex does give you good returns.