I was intrigued by the fact that sulfite and ascorbate showed almost identical curves in the excerpt that was shown in "The Theory.... " while hydroquinone showed no effect. Most simple analyses of MQ developers omit mention of the importance of sulfite to the "regeneration" of Metol by hydroquinone. The operation of ascorbate is certainly different in the long run from that of sulfite, and the regeneration of metol by hydroquinone appears not to take place without either sulfite or ascorbate. Ascorbate and Metol without sulfite, with the proper pH, can make a developer that is as active as Metol and hydroquinone with sulfite, which would lead one at least to guess that ascorbate is both developing agent and antioxidant.
IIRC, the antioxidant and the reducing properties of ascorbate use different parts of the molecule. The body does remarkable things with it to allow it to pass into the brain through the blood supply. We can use either ascorbic or isoascorbic acid in our developers, but the body needs ascorbic acid for vitamin C, from what I have read.