The zone system gives you an overview of how everything between film, exposure, film development, paper, and paper development exist in a kind of symbiotic relationship. Change one thing, and it gives you an understanding how all the other links in the chain may be affected.
As for the myth it will allow you to print everything on grade 2...check out Ansel's many examples in his books to see how often he used other grades.
No system is better than experience. Here's an example; you come upon a creek at dusk with a mountain in the background. The sun has set behind the mountain making high wispy clouds glow orange, and everything in the foreground is illuminated by deep blue skylight. You don't have long because the clouds are just moving into position and the mosquitoes are insane.
As you're setting up the camera you think, if I use a red or orange filter the foreground trees in shadow are gonna crap out, so a yellow one is probably better, but it's not gonna deepen the blue sky enough to make those clouds pop out, but that's OK because I'm not gonna give this one minus development but give it normal development because of the weak shadow contrast, so I'll expose and develop for the shadow contrast and let the clouds land somewhere around zone X or XI as they are orange and with the filter factor applied the clouds are going to expose the film proportionally more than any other element, which is OK because I'm gonna burn in the sky and the mountain anyway to get some detail in that glacier, so that'll darken the blue parts of the sky while I'm burning in the cloud detail and then those clouds are just gonna sing! Then you meter it to confirm your hunches, and add a bit to the filter factor just in case you're wrong about the shadow detail.
They don't teach that in books. (Like I really know what I'm talking about!)
Murray