I've dueled with an opponent that had an Exodia deck draw-based. It happens that he managed to draw Exodia, but in the same time that he decked out. Which win condition has priority? Exodia "effect" or deck out?
The deck out is irrelevant. The player drawing Exodia (and presumably completing the set in hand) has already won the duel.
Even if the player has not completed Exodia in hand, they do not lose until they are required to draw and are unable to draw. They may sit with an empty deck until next draw phase if there is nothing else to cause the duel to end.