This "Raging Sea" concept is beautiful, good thinking!
I like the "Drowning in Air" spell, which like Sailor's Death would fill the gills of an aquatic creature with gases.
Also, this is not specific to MA Oceania, as they're amphibious already, but it makes me think it would be nice if there were a ritual that would make a specific commander able to leave the sea AND bring some amount (10 or 20 maybe?) of aquatic creatures with them. This would be especially meaningful to EA Oceania and EA R'lyeh.
As for the mages, rather than a change that makes them stronger underwater (which may not be acceptable by design), at least make them similar to Slave Mages, where they only lose 1W, but keep their other paths. This is still really detrimental, but not a complete crippling of the caster.
Re: Suggestion for new Oceana units
Threaded Mode