But most of us were under the impression that it was the power of light actually making us immune to it. AKA, basically tempered by the Mothercrystal vs. evil Primal. Although the Echo being our resistence makes sense, too.
Also, I think Midgardsomr following us around to watch us instead will be a HUGE plot point. Minfillia mentions his job is, legendarily, to "guard the lake all magic flows," but is that exactly it or just Min's best theory?