The very point in confusion people starting on UE does when dealing with textures is because the way the nodes are used. For them TextureObject and TextureSample seems the same (you can select a texture asset at both), while they are not. The TextureObject Node is just an alias for the texture itself (the whole asset thing) while the TextureSample node actually is a processing node, which takes the inputs texture and uv and then sample the texture at that uv coord in the outputs RBG, R, G, B and alpha. I would rename the name from TextureSample to TextureSampler to clarify it a little more.
If one needs to use packaged textures with the built-in functions in Unreal which takes T2D as input, the best thing to do is to recreate those functions and inside use the channel where the target portion of the texture is to be handled in order to make it work ok.