textures definitely need factor of 2. It is called ‘power of two’ and enables mip-mapping. It is a standard feature in DirectX. It is pretty much the same in any SDK that uses DirectX/OpenGL, may it be Unity3D, Unreal, CryEngine, or here the Flight Simulator.
I tried again this morning. Simple cube from Blender with the gltf exporter. All there, gltf/xml/bin. Did it by the book, all paths seem ok. 209 Erros, did not work. Honestly, this the poorest SDK I have ever seen. Even their installer does not have a author. Author is unknown so Windows blocks it unless you permit exception. Where did they find the guy who developed this thing of an SDK?