They’re both really good (considerably better at what they do than FreeCAD is, to be honest), but they don’t do what FreeCAD does. Blender is for art, so that’s a different thing entirely. OpenSCAD does mechanical part design, but it only does mechanical part design. FreeCAD can do architectural CAD, BIM (Building Information Modeling), civil engineering stuff (e.g. working with survey data/site elevation), FEA (Finite Element Analysis), 2D drafting, stuff with NURBS and point clouds, texturing/lighting/rendering, CAM and CNC (i.e. toolpaths for a mill or 3D printer), etc.
nekusoul