I have seen and read many articles about PSA quality control issues. I have both the FN 57 but the one Achilles heel I hate about that pistol the slide is basically Blue steel and you can't oil it or keep it light then oil and under sweaty conditions it does rust

I also have a Ruger 57 but the slide is black oxide and rust very easily as well as the magazine so you can't carry that as well in human environments

The PSA Rock 57 seems to have a very good rust resistant finish on both the slide and the barrel except the metal magazines are like the rugers prone to rusting. Nevertheless I've got lucky with the rugers I had no problems with mine but other owners have and had issues from gun misfeeding rails breaking safety's not working

In almost every review I saw of the PSA Rock River 57 have been some feeding issues so I'm kind of reluctant to buy that not knowing it can be fully trusted for a carry gun

That gun puzzles me. On PSA's website it is described as a delayed blowback action. But when I saw the tear down during Sootch's review, I could not see how the blowback was delayed. You can see it clearly in the Ruger design.

Edited to add:

Never mind, I've discovered that the FN Five-Seven, Ruger 57, and the new PSA gun all use a funky spring loaded cam arrangement to delay the blowback.

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Release the Kraken

THe Rock's slide is stainless, so no worries there. Degrease the mags well, then coat with Rust-Oleum...problem solved.

I would sooner have a Ruger-57 Cerakoted or treated with some form of FNC surface hardening to prevent corrosion than buy a whole new pistol, in hope that it's more corrosion-resistant, but then again, if the Rock 57 is indeed Stainless Steel, then there's another matter.

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Shooting Comfort is bilateral.

But...........
Why carry a 57? They are big. Yes, I have a Ruger 57 and love it, as a range toy.

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Super Snooper

I'm not sure what you mean about the FN Fiveseven. The Fiveseven has a polymer slide cover that completely encases the steel slide assembly beneath. There can be NO more protective layer than the thickness of a polymer case so I'm somewhat confused when you say it "rusts."
If your Fiveseven is showing evidence of rusting under the slide cover then you're not carrying it in a holster, and so the fault does not lie with the gun, but with your expectation that you can carry ANY gun in close body contact sans holster (or some form of encasement), then blame the steel for rusting.

Even stainless steels can be made to "rust" in the manner that stainless does - blackened areas and spots, and depending on the alloy, outright rust.

The solution for you has nothing to do with the gun, but with your method of carry. The right answer is to properly insulate the gun from caustic sweat.