The Patch 5.2 Discussion Thread! (Spoilers)

[Naria]

The Echo seems to be a fragment of "the ability to inflict one's will on reality via aether". It is probably core to the Asican's ability to use creation magic. Therefore results could depend on the person using it, their particular talents, skills and experience, as well as what they are using it on etc. Considering Zodiark was summoned to restore order in a world being torn apart by uncontrolled creation magic (regardless on if that was the origin of Terminus or not), him being able to "temper" (exert order and control over) Ascians as a source of that magic is not surprising. As others of posited Zodiark's ability to "temper" could have been an unintended side effect of his purpose. Meaning that Zodiark was summoned to restore order not to control people's wills, but having no limits on his ability to control creation magic also allowed him control the source of that magic--the Ascians themselves.

Hydaelyn might not be able to temper as we know it but instead empowers people simply because she was summoned specifically as a counter to Zodiark so the ability to control creation magic was unneeded. There was, however, a need for a few to be able to overcome many.

All primals that we know of since the crystals were summoned as a result of Asican instruction. These instructions that might have deliberately designed and included a way to allow them to bind their worshipers to their will but not "control creation magic" so it could be overcome by the Echo. Basically we might be dealing with two separate but related phenomena that have similar effects but different origins and are therefore being mislabeled as being one.

Edit:
Just a random thought: Hydealyn has shown the ability to put "shields" around the Echo during the fight with Iggy and Lahabrea. Perhaps she has the ability to deny creation magic and insist no, this is reality not that. Zodiark controls while Hydaelyn negates--different methods to achieve similar ends. Perhaps her blessing instead of empowering her chosen is just negating/weakening the power of every Ascian or Primal we fight.