I still hold to the idea that Hydaelyn is a "fake," man-made Zodiark, but that doesn't necessarily mean she's evil or malicious. Just that she's a fake. The hypothesis here is that Zodiark was a jackass god, so the first men created Hydaelyn as a preferrable alternative in the same way beast tribes created the primals to deliver them from his jackassery.

Tempering? Well... from what we know, it's the Ascians who taught the beast tribes the summoning ritual, and that's why they tend to be jackass fakes of what they're intended to be (Good King Moggle Mog XII, f'ex). Considering that I find it likely that the Ascians can modify the summoning ritual to suit their needs, and the "tempering clause" is something that can be left out. Hydaelyn, being the very first primal, was one whose development was not influenced by the Ascians, since they either didn't exist or weren't aware of primals yet. They took Hydaelyn and used her creation to encourage the beast tribes to make their own "fake Zodiarks" in order to weaken her and bring Zodiark back.

Well, that's the theory anyway. (Patiently waits for 3.1 to debunk muh crazy crackpot theories)