A fellow ninja in my FC was watching my rotation and he (or she?) told me that if I have Dancing Edge up, I should only use Fuma Shuriken because "it does more damage than Raiton" and "Raiton cuts into Global Cooldown".

So I did some testing.
As for Fuma Shuriken doing more damage than Raiton, I never witnessed it happening, even with Dancing Edge applied. Unless I am reading or doing something wrong, I can't see Fuma Shuriken doing more damage than Raiton.

As for cutting into Global cooldown, yes it does seem to, but by so little. I imagine this is dependent on skill speed. The IL 250 crafted set gives unnecessary skill speed, which could be causing this. With less skill speed, wouldn't this go away?

Does the tiny cut into global cooldown make it worth using Fuma Shuriken over Raiton? Will lower skill speed reduce this problem? (Equipping gear without skill speed.)