Well, I don't know exactly what "coating" S&W uses on the 442 cylinder and barrel, but I assume that it is just a more or less traditional bluing. Bluing really isn't a coating but is instead a controlled oxidation process (rust). It is primarily cosmetic and really offers very little in the way of rust inhibition. Blued steel isn't much better than plain, bare, white steel as far as that goes. Especially if left "dry" (no oil) or is exposed to oxidizing agents. Hence the advent of stainless steel and a whole host of alternative gun finishes that has spawned the existence of many companies. While blued guns can be attractive, if they were really well protected from rust we probably wouldn't have near as many other options even available.
A pocket is not the best of places for carbon steel. Sweat has a very high salt content and salt, as anyone that's ever lived in the snow belt or near the ocean knows, is very corrosive to steel. Also there is the fact that many leathers can actually cause corrosion on their own due to chemicals (tannic acid for one) used in the tanning process. That's why it's never a good idea to store a gun in leather over the long haul. I've actually had a stainless gun rust from being left in its leather holster for a long time without attention. And yes, even "stainless steel" will rust. And then you carry a leather holster in a sweaty pocket. The leather absorbs your sweat, which then evaporates leaving the salt behind. After a few times of this the salt content in the leather can be very high. So, now you're storing your blued gun in a salt impregnated, often damp, leather holster for hours at a time, over and over.
I do believe that some people's sweat is worse than others although I don't really know why. Oils are not created equally either. There has been a lot of tests done on various products abilities as a rust inhibitor, so you may want to reconsider whatever it is that you're using. But, with that said, I believe that if you want a gun that resists rust when stored in a hostile environment like a sweaty leather pocket, you'd probably be better served to look into stainless (yeah, they can and will rust too) or an aftermarket gun finish. Bluing just ain't it.
Now, with all that said, I will also add that I have carried a Keltec P32 in a leather pocket holster pretty much since they came out. I sweat a lot in hot and humid GA too. Many times I've pulled the gun/holster out and the leather would be wet to the touch. I wipe the pistol and the inside of the holster down with oil on occasion but it is far from being truly cared for. Most of the original bluing has worn away and yet it really hasn't rusted all that much. Don't know why.
I guess what I'm saying is that I don't think this is indicative of a "fault" from S&W. Blued steel just rusts if you aren't careful.
Good luck solving your problems.