When starting out with any new or unfamiliar film, I'll shoot it in 120 roll film version first to save money, use a gray target, and will indeed cut the box speed in half, and then bracket exposures upward from there. Leftover frames will be used for the same kind of test with my favorite contrast filters. I think that kind of custom is common, reasonable, and a quick way to get to first base. So it's probably been stated in that manner many times before. Just makes sense. But any hard rule doesn't make sense. If you want the practical truth, you have to test each film yourself, under your own parameters.
Box speeds are sometimes trustworthy on a general basis, especially for color films, and sometimes they're not. I think many b&w films are labeled overoptimistic, and a few products downright deceptive. Marketing is generally part of the mantra. But as we all know, different developers can affect film speed differently, along with different degrees of development. There is no silver bullet generic equation for how to best expose film , and never will be. Anyone who teaches otherwise is a snake oil salesman.
I partially disagree with Maris because I think the Zone System is still helpful to at least understand in principle because it's contains a common-denominator vocabulary quite useful in a multi-generational sense on forums like this one. It's also a helpful introduction to practical sensitometry versus the more technical aspects. But like Maris, I don't pay attention to it during my own workflow.
Wilt - your habit of overexposing color neg film is based on moth-eaten old advice which can be counterproductive nowadays, especially with a more contrasty and saturated version like Ektar. People are often astonished to learn that many of my color prints are enlarged from color neg film. They look more like chrome results - clean, vibrant, un-muddy colors.