You might have noticed that sometimes the Export project option takes a while to complete, especially with larger projects. This is because Construct is working...
From what I can see, none of the image optimisations apply to images stored in the project files folder, is this correct? I have to use the project file folder in the absence of a 3D object "set face to use image of (by name)" action
That's right, images added as project files are just copied to the export as-is and aren't processed any further.