I dont think youll ever get the same quality as a factory finish. As if you sand back to bare metal, your taking the galvanising off, also the ED coat that the car gets dipped in during the paint process. The paint in the factory is also electrostatically charged, then it goes through big ovens.
The actual finished look maybe better from a bodyshop without orangepeel etc, but actual protection of the steel is never going to be as good,