Fusion by default smooths stl face normals when importing. This is great for smooth surfaces, but for planar surfaces gets very messy.
If you try to model a mechanical part from an stl, it gets very difficult to visualize the geometry with this shading.
In other packages there is an option of flat shading so you can see planar faces composed of many triangles as a single one.
This is how it is displayed in Fusion:
The same happens in blender when you have smooth normals on:
If you flatten normals, you get this: