There were multiple generations of successful studio photographers who didn't use the Zone System.
In fact, some of the leading pro photo schools thought it was just a quirk for AA and the "rocks and
trees" crowd. Rather, the lighting ratio in the studio was adjusted to the range of the film, and if needed a gray card was put in the scene or a Polaroid preview used. A simple outdoor trick was to
read the palm of your hand for Caucasian skintone. Of course, spot metering and some greater degree of sophistication in your exposure model would be a more flexible system. And the Zone System doesn't need to become complicated. It's not a religion.