Interesting conversation. If there is one thing I learned about kyokushin kai practitioners, it was to go for soft tissue - they've damaged their hands/arms and legs enough that subtlety will not work - deflect, evade, redirect if possible and look for ugly openings.
Ninjitsu punches are so slow as a deliberate handicap. The ninjas are just trying to give everyone else a fighting chance. Duh.
They're so slow because they don't want the stealth penalty for moving at more than half speed!
They're allowed to punch slow, because when you notice a ninja is near you, his fist is already inside your ribcage.
I miss karate.
Try aiming for the center mass and stop leading with your chin, it telegraphs your moves.
IS the punch itself supposed to be slow, or is the kata you are using to learn the punch slow?