I think the example of pregnancy is perfect actually and saying you are HFA is like saying you are 'a little bit' pregnant. You can put adjectives to the word 'alcoholic' as you can use adjectives to go with the word 'pregnant' Someone calling himself/herself HFA is admitting he/she is alcoholic. You can be on the first/second or third trimester of pregnancy. And each trimester comes with different developments.
I do not thing HFA is a label always and I don't think is really tries to prove you are a 'better' human being than the next alcoholic. You are alcoholics coping with the same probem in different stages or different circumsntances (I also believe that what some call HFA are lucky human beings with money and family to hide the lack of functioning).
Honestly, I find the expression useful for many people who are in denial because they are not fitting the homeless stereotype they have in their mind. Someone who understands that they can be alcoholics despite fulfillng their jobs/family duties, not getting consequences from the drinking, is not in denial. I cannot see how it is possible to say alcoholism is progressive and deny there are different stages for different human beings in different circumsntances.
I do not think it is a myth. I believe many people stop drinking before lifes becomes really touched by the consequences of their alcoholiksm precisely because they understand they are alcoholics nonetheless and that the consequences are not there yetI do not like the expression because I do not like the word alcoholic in general and adding adjectives just makes it more pathetic and shameful to me. Cannot imagine going around say 'hello, my name is Wilde and I am an HF/Bottom/whatever/ alcoholic.