Wolfish, If the bochor says he holds of a psak of a lesser shiur, who am I to argue with him? Of course I would respect that and not force him to drink more than he wishes! 🙂 And I would fully grant he is yotze the mitzvah.
But a Yid has a Chezkas Kashrus, and if he tells me he holds of the most common understanding of ad dlo yoda – to become intoxicated to the point of being unable to make a distinction between Arrur Haman and Baruch Mordechai…