Well spotted.The clip after that one seems to fit that assumption too, it seems like they're definitely going with the 2 weaknesses thing.
Although in that example you've pointed out, she didn't actually do that much damage. So I guess it's the same fairly weak advantage as in Awakening. Lol the same one I forgot about for my first 2 playthroughs and only remembered when I was on Insane difficulty (or whatever it was called)
To be fair, Kazahana's a low level
Samurai wielding an Iron Katana, so of course her damage will end up being lackluster. That said, weapon triangle bonuses only typically confer +1/-1 damage to the advantaged/disadvantaged (though since Shadow Dragon, WTAs also shut down weapon level bonuses which varied depending on the weapon type, namely Swords got +1/+2/+3 Mt, Axes got +5/+10/+15 Hit and everything else got +1 Mt/+ 1 Mt +5 Hit/+2 Mt +5 Hit for ranks C/B/A respectfully).