As a hobbyist - the CAD tools I've used (Fusion360 and Inventor) - are clunky with arbitrary 3D shapes (e.g. a Porsche door panel). How do people in the "real world" do it? Iterate in Maya / similar and then export? Think in parametric curves? Something else entirely?
An industrial designer would sketch the outline then the images would be brought into parametric CAD software as references. The 2D image can be built into 2D/3D lines, then these curves are used to create surfaces which finally are stitched together. The nature of complex surfaces interacting and joining seamlessly is where the difficulty lies. "A class" surfacing is an entire speciality and can take a career to master.
https://en.wikipedia.org/wiki/Class_A_surface
