All the fittings above the waterline are what is prone to rust and they would need painting frequently whatever they're made of. Below the waterline never rusts. Rust threatens above and around the waterline where the paint gets nicked and then the air gets in.
If they are made of stainless, you can leave them anywhere, above below, on a beach, you can scrape, or grind them, and zero corrosion at all. Including fittings. All of the thing, can be cleaned with a powertol and a fire wheel and in fact polished like chrome if you want as good as brand new 50 years on. A 100 year old boat could look the same as a brand new one. Without any previous maintainance. And thats why its value would exceed any steel boat when sold on after a yer, or a decade, or a century.
Another thing.
Barnacles... They cause corrosion, and they take £££work to remove. They add 15% approx to your fuel bill through added drag.
But the whole of the hull can be mirror polished if its stainless. The barnacles cant attack. Same with rudder, prop, etc. And so no periodic barnacle cleaning. And the polished hull will also mean less fuel/drag too.
All this is almost definitely true. But it will cost more initially. But ends in a superior product. And higher resale value.