[Stephen Benskin]

It is clear to me that subtleties of the cycle cannot be summarized by just a single gradient number.

And it was never meant to be. Just like the average driving speed in a trip doesn't specify the time spent at stop lights. It's an average. The average gradient, which includes the testing conditions, offers a general picture of the the way the film responds to exposure and development.

For any film curve, the average gradient for a 1.30 log-H range might be different for the average gradient if measured using a 2.20 log-H range. How it's measured is part of the answer. Think of the arguments for and against the various methods such as Gamma, Ilford's Average gradient, and Kodak's Contrast Index. And while we're at it, how much information about the film curve does a simple density range offer as some methods suggest using?

Once again, nothing's perfect especially when you are attempting to quantify a subjective response. And as with the NDR / LER relationship, what better course is there to follow.