Burst streak makes sense at least, since in your case it doesn't actually interfere with your damage output.
Better damage output with Fenrir and non 100% eido vs double elemental is news to me though, considering the maths so far have been telling me to run double elemental once my assault values go past 120%, and my water team is past that level. What's your water team's assault at?
My side, I'm just gonna do a few runs with Fenrir much later on fire rag just to see...