The distortion you see occurs because substance triangulates your model differently than blender does. This stands out more when you have straight uvs and curved surfaces with few loops. This is expected with models optimized for games.
To make the triangulation consistent re-Export from Blender your model to substance with a triangulation modifier on every object(triangulating when it exports) or export your model from substance painter under, file<export<model to get substance's triangulated versions and then import into Blender. I recommend the first, because the second will join any separate objects and has extra steps if you want to make future changes to your model.
Displacement only works in cycles and you are using enough geometry to displace and will only needlessly add to the normal map's effect when used for height.