The main issue with this is that Fuma Shuriken damage is boosted by dripping blades, while Raiton is not, since it is magic damage and dripping blades only boosts physical damage. If they would fix this so that dripping blades boosted all damage, then Raiton would be used much more frequently, even without a potency increase.

So Fuma is 288 and Riaton is 360. Raiton is still stronger but not really once you count the loss of GCD clipping. That said, if Raiton was intended to be stronger (given that it's a higher level skill), there's not really a point in using it, right? Unless the mob has a magic vuln debuff