There are all types of powder coatings, just like there are all types of paints. The resin systems in powder coatings can be polyester, epoxy, or combinations of the two. These systems can be designed to have a variety of properties.
Harley uses powder on frames and bodywork. This is not because of superior performance properties, but rather due to EPA air emission regulations.
As with paint, preparation is important. A poor powder application will be worse than a good paint application. Choosing the wrong type of powder or undercuring will result in a job that may have poor chemical resistance like Pommie John.
Because powder uses no primer to aid in adhesion, the powder must give superior adhesion to bare metal while still maintaining good gloss, hardness, toughness, and chemical resistance. That's a tall order. Usually the adhesion is not that good. That's why when you run a tap into the threaded hole to clean out the threads, you can create an opeing for oxidation to start. Also powder coaters should blast and clean the frame immediately prior to applicaton. If the frame stands after blasting for any length of time, rust will begin to occur and affect adhesion.
Powder does not have any inherent advantages over liquid paint.
These opinions are the result of 34 years of paint chemistry experience including several years involved in powder coating formulations. You are free to form your own opinions.