I attribute more of the quality of Adams's prints to hard work printing. If one reads his technical books carefully (particularly the margins where he describes what was done in the example image), many of his images/prints, including MOST of the famous ones, succeeded despite deviation from the techniques in the main body text. In many cases errors were made, or the negatives were made before the Zone System had been formulated, or when metering was approximate at best etc.

Considering the main body text would have you believe it is critical to expose and develop the negative with precision, to print on grade 2 etc, relatively few of the examples or his best loved images were made that way. His prints are all over the place, from grade 1 to grade 6. And in describing how the negatives were made, how often does he say "unfortunately...", "in retrospect it would have been better...", "I accidentally...", "I forgot...", "the cliffs moved into shadow during the exposure...".