Hey Casper Wermuth -
The Metallic and Roughness inputs for materials are essentially math inputs and will only read 0 to 1 values, which it looks like you have it setup to do. So the rendering of the material in the level is actually correct in order to get that roughness map applied to your Base Color you would have to multiply the two together then plug into Base Color and leave the single Roughness texture in Roughness.
As you were saying I have been trying to reproduce the issue of the material editor window showing you the incorrect render (essentially it looks like it is applying your roughness map as a overlay to the base color). Try plugging your material up as suggested above and take a screenshot of the resultant material editor window and level rendering.
Thank You
Eric Ketchum