Some more food for thought - Even if we can assume the initial part of the tempering process to be similar in all cases, or at least similar enough that the Echo can prevent it universally, once the tempering takes hold of someone the effects of the actual "changing" process could also perhaps vary from primal to primal. That would add an extra layer of complexity for attempting to revert a thrall back to normal. For even if one were to discover a way to reverse the tempering from the thralls of one primal, that same process may not work the same way for those enthralled to another primal. Given how we've noted that thralls react in differing ways based on the primal they're being made to serve, it wouldn't be unthinkable that the link that binds that tempering is enacted in differing ways as well. It could certainly be possible that there's no universal "cure" for tempering. But again, we just don't have enough info atm to confirm this is the case.