Yes, the power differences betwen LK and RK is huge. I prefer using 2 hand sword with krasnaya build, to maximize parry and atk power, considering it always do 100% dmg to all size.
Passive works on all weapons. You tested it wrong. It's not the same as the parry active. It doesnt show a block graphic and will not activate avenging lightning. What it does instead is it just ignores the physical attack you receive when it activates.