How did we not realize this about the man made echo?

[DPZ2]

After all we learn those two things are separate. And that it's the blessing of light that allows us to fight primals. Why else would sending Fordola fight primals work? Or Zenos fusing himself with Shinriyu?

Fordola and Arenvald can fight primals without being tempered because of the Echo. I do not remember coming across anything about the Blessing of Light for either of them.

The two things may be separate, but it is NOT the blessing of light that allows us to fight primals without tempering, it is the Echo.

The blessing of light prevented our deaths when Ultima was released (rather directly).

Thordan's aetherical dust is exactly the same sort of thing as the defeat of any other primal: the aether dissipates. He had neither the Echo nor the blessing of light.