What is ninjutsu? You can ask that about any MA. People are comparing ninjutsu vs BJJ or other arts, trying to answer what ninjutsu is. But it doesn't help because you can't name what any art is really. Just compare two schools of the same art: there will be big differences. Then to complicate it, each student has his or her own interpretation of the style. Going beyond just "what is ninjutsu", I'd say you define your own art by what you do with it, and how you interpret it through your own limitations and specialties. If you want hardcore sparring via ninjutsu--quit complaining and do it. Surely, there is someone there after class who wants to go all out, and test themselves with you after class. Get the head instructor to stay behind and fight with no pads (just wear a mouth guard!). Yeah, you'll get injuries, but that's a great feeling because you're delving into the art beyond some of the stale training methods that seem to limit ninjutsu. Don't blame the art, blame yourself and solve your problems. If no one at that school will work with you, move on.