No power ever comes from the right.
That is why there are warm up exercises using katate (single left hand warm up) to loosen and focus on your left.
It makes no sense for power to come from the right as fumikomi (the leaping motion at the time of the strike) is done using your left hips and legs.
Ah, I think that is a typo, otherwise the whole comment doesn't make sense and my brain corrected it.
The explanation I've heard is that in any sport, on average one would train more with right-handed opponents. So when facing a left-handed opponent you are significantly less experienced, which results in left-handedness having a slight advantage.
That is a bit different than what you describe (since you're not allowed to use your katana in a left-handed fashion), but still.
> You have to wield your sword like everybody else
This right here is why.