The model you suggest is not far from what we have. The main core types of materials are conductor & dielectric. The complex material may end up being either of these, depending on the nature of the complex IOR data. Conductor represents a reflective (opaque) surface, and dielectric is a reflective/refractive (transparent) one.
Separate from these we then have the subsurface material, which like dielectric is reflective/refractive, but which simulates subsurface scattering using the fast random walk method.
Over any of these substrates may be placed a layer, but a layer may also be used on its own as a material — this is the sheet type: a layer, used as a material, without any substrate.
Building on these core types we then have the “smart” types, which expose just a few parameters, and build more complicated materials internally, from those parameters. These cannot do anything you cannot do with the core types, but they can save time & make things simpler when maximum control is not needed.
What I refer to above are two further types, which also build on the core types, and which can be made as complicated & all-inclusive as we wish.