About the Echo (Spoilers)

[Absimiliard]

The evidence against that (based on what we know about tempering) is pretty clear-cut, though. (Namely, people with the Echo very clearly working against Hydaelyn.) So the usual counter-argument is that maybe tempering doesn't work the way we think, which is possible, but lacks any real evidence other than "what if".

If you mean Ysayle, she legitimately believed she was serving Hydaelyn's greater good through her actions. We've actually seen several examples of tempered beings going against the interests of their primal out of misguided belief. Tempering does not come with a set of instructions, and the individuals are not necessarily beholden to act only at the behest of their primal. The blind loyalty tempering inspires has lead to all manner of unintentional defiance by those believing they were serving the primal's intended interests.

Similarly, we've seen and heard of people with the Blessing of Light work against Hydaelyn too. Ardbert and the Warriors of Darkness are the main examples brought up, and there's also Saint Ajora in Ivalician history, who was a Warrior of Light who unsealed Ultima the High Seraph, which is probably something Hydaelyn was expressly against.

Ajora did not unseal Ultima, as it turns out. He was the one that summoned her in the first place. However he managed to do it, the implication was that his destruction of Mullonde was actually accomplished via that very summoning. We can't guess as to his motivations due to having no information beyond the fact that he did it, however.