I've considered this idea, that we are tempered by Hydaelyn. It would explain why the other primals can't temper us, and iirc, Garuda does say something akin to us being touched by Her. We do seem to do whatever it is the giant crystal asks of us. Sure, we seem to have more freedom than others who have been tempered, but maybe that's the difference between a powerful entity like Hydaelyn tempering us and a lower primal. Lower primals rely on brainwashing. Very straightforward. Hydaelyn has more power, so she doesn't let us know we're tempered, but simply guides us and nudges us in the right direction, all the while we're convinced that we've got our own free will and are doing Hydaelyn's bidding because we WANT to....