You problem, Noctis, is hanging on the 'primary' somehow being 'only', 'exclusive' or 'single'.
If there are Dungeons, Grinding, FATEs, Leves and Quests, and quests account for 35% of the XP intake, they are still the primary means. But they are hardly the 'only' way. We can only make a judgement come beta and we truly discover what 'primary' means.