SE I am disappoint (Possible Spoilers)

[Ibi]

The triad do somewhat have a role, during the Singularity Core, it's implied that the king uses their power to summon his knights for Ultimate End, when he tells his sword to "drink" deep.

Hmm. I assumed it was Nidhogg's Eye he was telling them to drink deep from, given that when he first transforms into Thordan he says his "being is sustained by a millennium of fervent prayer and the Eye's nigh bottomless reservoir of aether."

Urianger's text in Gods of Eld isn't explicit, but does suggest that they were tapping into that power, since his defeat had an effect on them: "'Twas first and foremost to acquire the infinite power of the Warring Triad that the archbishop did seek Azys Lla. But in the wake of his defeat, the bindings which confine the eikons were severely damaged."