The following is an excellent example of what I think of as a somewhat realistic samurai sword fight, with blood. This scene is probably from Zatoichi by Takeshi Kitano. Three blows parried and one blow not parried, and the fight is over.
I doubt that many people will be surprised to hear that a cinematic sword fight is not realistic, but the important point to take away is that it was never intended to be.
The same criteria should be applied to visual effects, whether what is being shown appears to be realistic or not, the important question is how does it serve or advance the story?