Your question really is comparing two very different approaches. If you "correct" the paint I assume you have imperfections such as swirls, scratches, haze, etc. These imperfections must be eliminated by proper polishing before waxing. Then, applying a coating like gtechniq, you're adding a layer of protection. This approach will not aid in rock chips, paint scrapes damaging paint, etc.
By applying a clear film, ppf, you're now adding a urethane film that protects agains rock chips, etc. You will still have to properly maintain the film. The better films, XPEL Ultimate, have self-healing properties that resist bird droppings, etchings, and swirls. This film is very optically clear, but as mentioned before, if you look very close, there is a slight difference between paint and PPF.
So, in the end, it all depends on what YOUR needs are.