About the Echo (Spoilers)

[Absimiliard]

I seem to recall the game telling us that every Ascian has the Echo. With how rare the Echo normally is, I would find it strange that they all would have it if it hadn't been a part of the makeup of the original Ancients. Then again, it could be that only those with the Echo (or something like it) were eligible to be a Convocation member. There's just too much we don't know.

... Then there's that whole argument about whether or not the Echo itself is a form of tempering that comes with a few extra perks. It is alleged to protect from tempering, yet Zodiark tempered the ancients? This would mean that, amongst other possibilities, either:

A.) A sufficiently powerful primal can temper you through the Echo.
B.) The Echo really is just an extremely powerful form of tempering exclusive to Zodiark and Hydaelyn.
C.) Zodiark has a unique ability that allows it to temper you even if you have the Echo.

The Echo user = Ancient soul theory essentially requires that one of these three things be true, otherwise a portion of the Ancients being tempered (and the fact that their modern fragments are still tempered) makes little sense.