I was not familiar with these grades, very interesting reading and finding out about them. The most common grades of stainless I have encountered in the marine industry is either 316 (best) or 304 (budget, requires regular cleaning to keep rust free). Both have issues with crevice corrosion and are also very expensive compared to zinc-plated equivalents (which I would never use on a boat since they will effectively disintegrate over a few months). Marine grade stainless often suffers from crevice corrosion and hard to detect failures which is sort of terrifying when you really think about it (things look OK until one day they break without clear visible warning).

For bridges or large-scale industrial applications where you dont care how the metal itself appears, I agree that coatings (especially galvanization) is the best bang for the buck. All of my insights are purely anecdotal though, as a hobbyist...