The way knife defence was incorporated into my Shotokan training was more and extention of the basic 1-step kumite i.e. the big lunge attacks are archetypal. People don't attack like that but reducing any attack to it's basic elements allows you to train core elements like footwork and timing study what is effective and what isn't. The key is simply to gradually reintroduce the complications of reality. Doing so will let you learn not just what works but also why. When we wanted to go beyond the reductionist training drills we picked up practice knives and tried to murder each other. We stopped when we were forced or when we knew we'd been tagged well enough by the blade. There's no comparison between the two methods when taken in isolation but as parts of a progression they work well together.