What is the question? If the MC is wet location rated, doesn't that encompass damp locations?
I looked at the MFG page for the Southwire MC-XHHW (one of the wet location MCs), it says that is an XHHW-2 conductor and that conductor is listed wet and damp (330.10(A)11(c)). I assume you would derate from the 75c column in a damp location like you do in a wet one.
The box of EZ-MC I have says you derate at 75c when wet but that is not exactly the same stuff. Southwire did not even reference that on their page. Maybe it was a THHN/THWN product that was replaced by the XHHW
The aluminum armor is considered suitable for wet locations if the wrapper and conductors are wet rated. I understand that salt air can eat it but when you are talking about the sea shore, galvanized rigid metal is not that great either.
Carrying that thought further, any aluminum bussing installed near the ocean is at hazard for AlCl3 'rust.'
Aluminum is normally considered 'rust proof' because run-away corrosion does not occur -- unless chloride ions are present.
But, aluminum is, in fact, prone to ultra-rapid 'rusting' / oxidation. Bare aluminum metal oxidizes promptly in air. It acquires a THIN coat of Al2O3 -- aka alumina. It's so thin that you can see right through it. Unlike iron oxide rust, alumina expands to lock up tight, creating an air tight seal.
If salt air is misting in, the chlorine displaces the oxygen in the alumina. Now the metal loses its sheild. AlCl3 shrinks like common rust. Given enough time, aluminum metal becomes pitted -- with cruddy AlCl3 ( it's yellow ) crystals at the surface.
I've witnessed bussing that's picked up a 3 volt drop right at the rails (under load) over a twenty-year period.
The solution is to kill power, buff the crud off the rails, clean the breaker-rail contacts and re-assemble.
Where it's an issue, copper bussing is worth the premium. Copper does not rapidly react with salt air like aluminum.
This issue is why aluminum can't be totally trusted below grade. Some American soils are absolutely laden with old ocean salts. (Nevada, California, Utah, Arizona,...) So you can't trust aluminum to stay bonded as part of a GEC system.