Really? hang on, let me check. Oh my bad, must be getting confused with another GO. What I meant to say *ahem* was use the trigger to cancel the first overdrive (to save on damage), reduced by kaiser. Then tank the raging overdrive multi-hit with Kushinada/Oto-hime.
It's weird to me that you keep saying Arthur is the weak point, when IMO, Arthur is one of the better souls out there. Not on par with damage/toughness as Herc, and not as good supportive as Shingen, but a nice combo of both when your team isn't ready for the super fast meta. Also, I've found, as many are saying, that the pots are plenty good enough. I usually have several to spare by the end.
To put it in perspective, my water grid and water team is pretty much a disaster even for a f2p player back during crom. My grid back then was full event weapons, with at least 3 SR (maybe even 4), before Water UE/Rahab reprint "saved" it (granted all of them were max skill level since I'm an old player). My team was soul with ambush, belphegor, atalanta, kushinada, oto-hime, using jack frost and a friend rudra. Zero healing whatsoever unless you consider Joan's regen on one of the mission (which is no better than sr nike). The only remotely difficult thing I have to get was a water kaiser (I thought I'd try to prepare a little bit for fire tower, even if it was pretty hopeless) and +99 eidolons, both takes a few months to get. Using kushinada/oto-hime combo and burst to tank/burst away the dangerous multi hit enemies (really look at their skills for a second, and you'll understand why, this combo is basically gaia level useful - granted, takes 2 himes). I got the full 20 points and all oris from crom. Really, if I can do it, anyone with a decent grid should be able to.