This was probably discussed heavily before but I may have found a time to use fuma over Raiton.
In my opener that I created, I have a mch buddy that I raid with, I use that physical damage buff a lot. So that means that with all my buffs up in my opener, I have DE + B4B + poison + phys vuln up from mch compared to only B4B for fuma. What I also do is I suiton at the start and let the mudra come off cd before using Kassatsu so I get two fuma shurikens buffed by B4B + poison + DE (360 pot*2) compared to a fuma + raiton buffed by B4B (360 + 396 - 1 sec gcd).
Here is a video of me doing the A7S dps check with the opener I described. It also explains that since I don't use Raiton, I lose as little gcd time as possible meaning I can also get one more attack in at the last second.
I slowed it down a bit so it's easier to see.
https://www.youtube.com/watch?v=C8Yr...ature=youtu.be
In this scenario, if it's just a straight parse with a mch, is it even worth using Raiton?