So are you saying the zone sysem is no longer as relevant as it once was? I'ev no doubt the Adams books are worth reading regardless.
I'd say it's relevant, in the same way learning how an automobile engine works is relevant. You can run your machines much better if you understand the mechanics.
In music, for example, you can make a nearly perfect trumpet sound with a keyboard now. I'm told it's lots easier to do it well if you know something about how to play a trumpet.
The Zone is a way of categorizing light and the response of film emulsion to it. It seems to me that understanding the how and why makes it much easier to use any real or virtual emulsion well. The division of light into ten zones is arbitrary but sensible, given the nature of the medium. Some sensors have a wide dynamic range, many are narrower in range, and there's always HDR, so the usual low end cut-off at Zone Three may or may not be valid.
But light and knowledge of it is always valid, and Adams knew more than practically anybody about light. "Moonrise..." was shot by feel, with (I think it was) an 8x10 view camera, in one setup, made in only seconds after stopping his car and piling out at the side of the road. That takes skill, and that takes some serious practice time, and strong theoretical study.
I've heard it said that the Zone is not as important with color work, and I think that a rigorous application is maybe overkill, but knowing the system, and knowing your 'emulsion' is vital to good success. As you study, you'll discover that Adams expected to manipulate in the darkroom, and his system is geared to producing a negative that would result in the desired print after that manipulation, and that's the strength of the zone. He made notes on such things as where the print, or even the negative, needed to be rubbed with a finger to work in the developer, and where a bit of cheesecloth on a dodging wand would be needed, and he did this in his field notes -- not from surprises in the darkroom -- as he planned the exposure from the beginning.
The system is partly driven by the need to conserve supplies. Even in the mid-1900's, an 8x10 negative was a substantial investment, and print paper was not cheap, either. Nowdays, we can flail away, firing an exposure every tenth of a second at no increase in cost. Except: Time is money, even for the hobby shooter. And there is -- to my mind -- nothing much more satisfying that to see an image come out of the printer for the first time, looking very much the way I wanted it.
One thing to bear in mind is that b/w film -- negative film in general -- has a wider range than transparencies, and so from the ascendancy of Kodachrome onward, the zone was sometimes treated as unnecessary because you couldn't manipulate color film in the developing tray, and for years most of us couldn't make prints from slides. Slide film is very prone to blow-out and so the emphasis changed. No longer were we as concerned with digging out the shadows, but with holding on to the upper end. With virtual film, the shadows become important once again.
Most other books on the system are recipe books; do this and this and that is the result. Adams' books are much more theoretical, though with practical application always in mind, and so will teach you better than another might, if you study, and think and shoot while studying.