Most of you probably know how Steiner's glitch goes: Thunder Slash is broke, and it isn't intended to be because Beatrix's works due to being a separate version of the same ability. I got down to business and finally found a fix for this. Turns out it was never Power or Accuracy and it seems the rumors about Iai Strike having anything to do with it are moose hockey, it was simply assigned to the Gravity Magic damage formula by mistake. Thunder Slash by itself shares all the stats as Steiner's other damage abilities: no inherent accuracy (which is why it was missing constantly under Gravity), similar power levels, in general nothing majorly deviates the norm for weapon attacks in his more powerful A-Abilities.
Here's a small patch that changes it to Magic Weapon like Climhazzard. TS is slightly in the middle of Steiner's direct damage abilities, doing damage to a single enemy that's more than Stock Break but slightly less than Climhazzard and much less than Shock. These are your standard PPF patches, use them on a v1.1 US PS1 edition (I don't think the PC release fixed this one, but I'm not 100% sure).
RHDN link (http://www.romhacking.net/hacks/3182/) in case the attached files don't work for whatever reason (also has Bin info).
No, the PC released didn't fix it; it was mentioned in the same exact topic on Steam I read about the whole "status accuracy" thing being linked with 0% hit rate VS "weapon accuracy" (which overrides said 0%). It also mentioned the ability being pretty powerful, so this does sound accurate.
Still, nice to have a patch for it!
In a strange turn of events, changing TS to Physical actually nulls it's element. This is probably because Physical Strike uses the weapon's element, while Magic Weapon carries it's own. So Magic Weapon is the only option now.