My current hypothesis is that Krile was captured and used to create the Resonant by extracting bits of her soul and transfusing them into whoever they wanted to achieve Resonance. There has to be some specific reason they went after Krile and held her where and as long as they did. This does invalidate the "Hypertuned are just failed Resonants" hypothesis, but I'm fine with that.
My current hypothesis is that Zenos achieved Resonance either shortly before or after Fordola did; he did not display the abilities he has in Ala Mhigo during our battles at Rhalgr's Reach or Yuzuka Manor and has two Resonant Eyes instead of just one like Fordola. The battle at Yuzuka Manor is more important for this - he has Ame-no-Habakiri there as well, but never uses Art of the Sword...