I wasn't suggesting that the Zone I test told anything about tonality on its own, just that achieving the desired tonality is the goal of using the zone system, and maximizing the full density range was part of the goal.

It isn't entirely irrelevant, because if you place Zone I too high, and for a certain lighting situation you want N+4 (presuming the film is capable of that, which was more likely in the early days of the zone system), then you might not be able to get it, because you will have "wasted" the toe of the curve or effectively, you will have reduced your Dmax.