Passivated stainless has been treated by some process, such as acid immersion. This leaches the ferrous ions from the surface & leaves a skin of pure chromium, which is rather inert chemically and is not prone to rust. If you scuff that surface, the passive skin is ruptured and the protection is gone from that small area, until it is treated again.
Crevice corrosion occurres when oxidation gets past the passive layer and then works it's way down the lattice of ferrous ions in the alloy. This corrosion happens behind the surface where you can't see it. The strength in the alloy comes from the ferrous structure, so once that has been oxidized internally, you will have a structural deficiency. The next time you present a heavy load, the part will break and then you will have a front row seat to seeing how much of the part was compromised internally. The shiny portion at the break is the portion that was still good. There are tests, like magnafluxing, that can spot crevice corrosion in it's early stages. Noticing it with the naked eye is a bit of a trick. Just to complicate it further, if rusting steel is nearby & water carrying that rust drips onto the stainless, you can get rust spots that stick to the outside of the chromium skin. These make it look like the stainless is rusting, but cause no actual damage, as long as the passive surface is still good.
Higher alloys of stainless have greater natural corrosion resistance without the need for surface treatment. Even without surface treatment, lowly 304 still has much better corrosion resistance compared to carbon steels, like grade 5 or 8. This is why carbon steel bolts typically have either zinc or cadmium plating. Bare carbon steel loves to rust
Those electronegativity charts, also known as galvanic charts, or nobility charts, become more important when the two dissimilar metals are in the presence of an electrolyte. Salt water is an excellent electrolyte. Rain water, and common tap water are not nearly as active, but the activity is still not zero. I don't know how active wet grass clippings are.
When using anti seize with stainless, consider the metals that are used in the compound and see where they fall on the nobility scale. Most anti seize is based on nickel and gallium. Some is copper based. I use grease when temperature is not an issue.
I think that the big question is - how have your fasteners been failing? Optimize against the most common risk by choosing the material that is least susceptible to that mode of failure.
To dumb down my response a bit - I would most likely just use 304 until I found an actual real-world reason not to. If I didn't see an actual failure myself, I'd stick with the stainless on the deck.
As an afterthought, adding rubber washers might help with electrical isolation, vibration damping, and covering up scratched paint.
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