IMHO, the "metal grind" paint treatment is a fad that came from the show bike circuit, where the paint doesn't have to hold up and the bikes don't have to actually run or be able to be ridden more than a hundred yards if they do actually run.
It is not necessary to actually break the paint film to have the result you have. And it doesn't necessarily mean there was moisture in the air supply or on the metal when they sprayed it. There really are very good reasons why we in the auto industry use galvaneal metal in the body panels, then we clean and acid etch the bodies, then we phosphate coat them, then we dip them in tanks of electrocoat primers, then we apply spray primers, then we apply basecoat (color), and then we apply multiple coats of clear urethane. Trust me, if it was just as good to throw a couple coats of clear on bare metal, we would have saved billions of dollars in facility, materials, and labor costs over the years and just shot the raw steel with a couple coats of paint.
You asked for opinions, so here is mine. Get a real paint job using a full conventional process if you want durability. Anyone who guarantees they can do a grind/clear paint job without such a failure is likely to be very uninformed at best, or a charlatan at worst. There is no magic.
Jerry