In A.A. parlance, the matter of "unable to manage our own lives" is related to our powerlessness to stay sober while sober and has nothing to do with how well we either do or do not function while drinking. Overall, two things here:

The difference between certain types of hard drinkers or heavy drinkers and the alcoholic is that the alcoholic has lost all control over how much s/he drinks while drinking. In contrast, the typical hard drinker or heavy drinker actually *can* control his or her consumption if/when s/he truly wants to do so and even if a little help might be needed to get there.

As to functioning: I used to be quite functional while drinking and there were people who never had any idea I was even drinking. In contrast, it is the non-alcoholic who typically cannot function well while drunk. Where the non-alcoholic might begin to feel a bit uneasy or out-of-control after having just a few drinks, at least some of us alcoholics are/were at that point beginning to feel quite good or confident and acting as if we are in complete control.