Bad hangovers are pretty much a mild version of alcohol withdrawals - that's where the whole "hair of the dog" thing came from.
Physical dependence on alcohol is more about regularity of drinking than amount - as with other drugs, your body can become used to small, regular doses and protest when they're withdrawn. Over time your tolerance will build and it will also take larger amounts of alcohol to achieve the same effect.
I do know someone who set out to become an alcoholic at age 23. He's 51 now and has been effectively homeless for years. He's literally dependent on the kindness of others to have a roof over his head and is incapable of basic daily living activities like showering and food preparation. His balance is severely affected by alcohol-caused brain damage as is his eyesight.
Realistically, he will be in a nursing home by the time he's 55 because no-one can stand living with him for any length of time. He showers only once every couple of months, he wets the bed, and he basically has only two or three conversations, all of which are about things which happened years ago.
I don't know a lot of alcoholics who drink more per day than the average person would drink on a binge, but income limits the ability of the ones I know to drink as much as they'd like. All of the ones I do know will have the shakes by mid-morning if they have no alcohol and several have had seizures or been hospitalised with the DTs at some time when they've been unable to obtain any alcohol.