The pinch of sulfite is to remove any oxygen from the water and to protect the Metol while it is dissolving. This is a small problem but using the pinch prevents the Metol from becoming discolored. It doesn't help with the Metol dissolving. Once the Metol is dissolved the rest of the sulfite can be added.
Trying to dissolve Metol in concentrated sulfite solutions is difficult needing heat and lots of stirring. Excess stirring introduces oxygen into the mixture and is best avoided.
In "two bag" formulations there is usually some sodium sulfite in bag A. Besides the problem during mixing the sulfite also preserves the developing agents while in the bag. As PE pointed out, Kodak spent a good deal of research on packaging and holds quite a few patents on this matter. This allows them to use a single bag package.