Except Ferne actually confirmed the column of light at the Battle of Silvertear Skies (i.e. in 1.0's original opening FMV), really was the Primals being released from confinement, and that until that time they had been sealed within the lake. This confirmation is in the 1.0 forum archive so it will take me a bit of time to dig up. But the important this is, the Primals were sealed until that point (which coincided with the first appearance of the Ascians to the beast tribes masquerading as the 'Paragons' and teaching each in turn to summon, Ifrit being the first.