Mea culpa. Based on my experience, they should resist rust better. Like the ad above, painted bare metal just pales in comparison to a heavy phosphated and baked enamel finish. That ad says 500 hours salt spray. My experience with that process and paints circa 1990s, is more like 1000 hours salt spray minimum. It's still not as good as galvanized under the paint, because that has an additional protection such that even a scratch through the paint down to bare metal, doesn't rust, as the large exposed zinc coat prevents it as a sacrificial anode. However I can't recall if painting over the zinc negates that effect, unless the inside surface, like with car bodies, is left bare of paint. Also, hot dip galvanizing is superior and used on things like anchors and chains in salt water, but adds weight to thin metal and has a surface finish of large crystals that prints through the paint, unless it has been "galvannealed" with a subsequent bake, resulting in fine grain surface and paints better. But I personally know of auto parts that were galvannealed that were later changed to phosphated and baked enamel, it performed so well and at lower cost and environmental issues. So, I have little doubt that Parker process frames had more rust resistance, provided the paint is also durable. If the parts are subjected to abrasion and deep scratches, galvanizing may still be superior.