You made more than just good points and for the most part I agree with you.
If you think about it, the entire reason I have come up with would be resolved as soon as the marketplace provides enough information. I don’t expect the author to tell us how everything works, but prove that it works.
The Unity-Assetstore has a package browser in which you can look at the included assets and most assets provide a web-demo too, that’s almost enough information for me. Details about the texture and if it’s PBR or not should be also included (maybe also how the PBR is achieved, something like “Masked Texture used for Roughness/Metallic output” or “Individual Textures are used”). I don’t expect the creator to tell me in detail how everything works, that’s too much.
I can’t think of a reason why a creator would want to hold back these informations/demonstrations.