Howdy
I think you are laboring under a bit of a misconception here.
When Ruger first offered the Vaquero models in Stainless, they were offered in a slight matte finish. However Ruger quickly realized that a highly polished Stainless finish would look very similar to the nickel plated finishes that were somewhat common in the 19th Century. In those days, Blued finishes were not as robust as modern blues, and the blue tended to wear off fairly quickly. It also did not provide a whole lot of protection against rust. In those days, a nickel plated finish was sometimes better protection against rust than a blue finish. However it was also fairly common for a nickel plated finish to flake off, revealing the bare steel beneath, which could then rust.
Ruger began putting a high polish on their Stainless Vaqueros and has ever since, to mimic those old nickel plated guns. However, that's all it is, the bare Stainless is polished to a mirror finish. All Stainless steels are corrosion resistant, because of the presence of chromium in the alloy. When exposed to atmospheric oxygen the chromium forms a passivation layer of chromium oxide. This is a natural process. Scratch the steel and it will 'heal' itself with a new passivation layer. The passivation layer is invisible, but it prevents atmospheric oxygen from reaching the steel, so it prevents corrosion. There are many, many different alloys of Stainless steel. Some are more corrosion resistant than others. The stuff Ruger uses is very corrosion resistant.
Blue finishes on the other hand are a chemically induced form of iron oxide, or rust. The blue is a very thin layer of oxide that forms on the surface of the metal. It's just that it is blue colored, not red like most iron oxide. In fact, another form of rust prevention on guns a couple of hundred years ago was 'browning'. This was another controlled layer of rust. This thin layer of oxide prevents atmospheric oxygen from reaching the body of the steel, and so it also prevents rust in the normal, red, fashion. As I said earlier, old time blues did not always protect the steel real well, they rubbed off easily.
Ruger's modern blue is very robust and protects the steel very well from rusting.
Of course, any blue will eventually rub off. I shoot a lot of Cowboy Action with Rugers and other guns. This means carrying holstered a lot, and drawing and reholstering a lot. Most of my Cowboy guns are blued, and most of them have some of the blue rubbing off on high spots like the muzzle from holster wear. Draw a gun enough times and you will get some wear on the blue. Then you have a little bit of bare steel. The best rust prevention for bare steel is oil, but I will tell they truth, I don't oil my guns very often, and I don't have any rust on the spots where the blue has worn off.
P.S. Before somebody tells you that Stainless is easier to clean than blue, let me tell you it ain't true. How difficult a steel is to clean depends on how highly polished the metal is, not the specific alloy. The shinier the metal, the easier it is to clean. The duller the metal, the more microscopic pits there are to hold dirt and fouling. It takes the exact same amount of elbow grease to clean a stainless revolver as it does to clean a blued revolver, all other things being equal. However a bright Stainless finish may tend to highlight fouling while a blue finish may tend to hide it.
Lastly, a polished Stainless finish may throw glare in your eyes in bright sunlight. I used to blacken the rear surface of the front sight on my Stainless Vaqueros for that reason. Basically, light sights will show up better against dark dark targets, blue sights will show up better against light targets.
You pays your money, you takes your choice.
