If Raiton never clipped the GCD, Raiton would be better nearly every time (mobs with magic resistance or immunity, or the incredibly weird case where you are in range for shuriken but not Raiton would be the exceptions I can think of). But videos or it didn't happen :P

TA is not factored into this guideline at all. And looking at the math, he's calculating the debuff as 111% damage instead of the 110% damage it is. He's also using a GCD of 2s for estimation.

Not sure whether it alters the conclusion, but those last two definitely skew the math in favor of shuriken.