Here's a simple cube created with Blender Render in Blender 2.79. Only Parameters given within Blender were Diffuse and Specular, colors, and Hardness level...Through the old tool FSX/P3D params is set using default settings (i.e., no transparency or special functionality.) so just trying to recreate something like this within the model material with the 2.83 Spec Shader without creating specific textures.
Let me make sure if I got this correct or understand what you are referring to? You are referring to just materials not being passed through to a model? is that correct?
If so, you are correct... as of this time, only textures are allowed to be made into a ".mdl" file. @Vitus has started working on that and hopefully will be available in the next release of the Toolset. Also, I do not know how far along he has gotten on it, though if I understand correctly, it was going to take some time to do. I personally agree with you that it should be. You should be able to check the model within the sim without textures.
Hopefully, Vitus will answer on the status of adding it shortly.