The amount of solvent action in developers depends on much more than the concentration of sulfite. Also, comparing the solvent action of a single bath developer to that of a two-bath developer is comparing apples and oranges. In D-23-based two-bath formulas solvent action will be significantly less (even with 100g/L sulfite concentration) than with stock D-23 because overall development time is shorter. This one reason (along with the relatively high pH in the second bath) why even "fine grain" two-bath developers typically produce higher graininess than single bath solvent developers.
Any modification to a balanced formula requires careful testing.