The IGN source isn't accurate about Jinpu (haven't read much else on it, but it doesn't look very reliable from what I read

). There are more accurate sources floating around with the numbers for Jinpu like archived gobli pages from '08:
https://web.archive.org/web/20080324192 ... es/64.html150Ex 五之太刀・陣風 +0.50 +0.75 +1.00 2 STR30% ダメージ 風属性物理
I think your IGN page's 1.5 number might've ultimately come from misinterpretation, .5 (first hit) + 1 (second hit). I believe the way it should function for this WS (and a few other GKT, Katana, and ranged WS) is the physical half of the WS is calculated normally (technically slightly weaker than Enpi at .5 + 1 vs. 1 + 1) and then the physical damage of all hits is then turned into the base magic damage, recalculated (resists, MAB, etc) and then they are added together.
Y/G/K seem mostly fine IMO, the reason I said most SAMs wouldn't like the answer about non-very high level targets is because they're likely dealing slightly more damage than they would have in era.