Quote Originally Posted by Cilia View Post
It's just vague what's doing what until Venat tells us verbatim in Endwalker, not really retconning anything. Ifrit attributes our immunity to tempering to the Blessing, but everyone else says it's the Echo (likely because they don't know any better). Raises the question of how Resonance works, but.
The effects of the Echo and Blessing definitely got retconned/reversed/forgotten-and-reassigned somewhere between Heavensward and Endwalker.

Midgardsormr sealed the Blessing of Light and apparently left us with only the Echo, which apparently stopped Hydaelyn from speaking to us, but we were still shielded from primal influence.

From the same era, the first lorebook seems to attribute most of our powers to the Echo while linking the Blessing to receiving direct contact or power-ups from Hydaelyn, like being shielded from Ultima.

That said, I don't see how reversing them makes Venat look any better than leaving them as they were earlier established. It seems more likely that they somehow forgot that they had established the difference already, because it seems too big a thing to deliberately rewrite.