[quote=Leidenschaft]
I think this whole argument itself on the presumption that they have met an opposing army in a land war. Provided with the current political climate of Tamriel, The Dominion has more than likely pulled most, if not all of its forces out of the mainland and back to the Isles. Given this probably highly possible scenario, no force in all of Tamriel would be able to stand a chance at crushing Alinor, short of recreating the All-Flags Navy sans Alinor, that is.Given the way magic is, was and has been used within the lore, any forces at sea would be pulled under by summoned whirlpools, blown off course by summoned gales of wind and ambushed in summoned mist by the hilariously superb Altmer navy. It would take a very, very skilled enemy to beat the Altmer at sea, and the only time that the Isles have been invaded, it took a CHIM-Having Dragonborn Emperor holding the leash on a Time-Breaking Mega-Robot built by the Dwemer.
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Historically the only people who come close to matching the Altmer at sea would be the Redguards, due to their seafaring heritage, people often forget just how formidable they are in the open ocean. As one must remember that before they came to Hammerfell, they lived on a sprinkling of islands, and if not for their seamanship, they might have never survived the destruction of Yokuda. Once they did take Hammerfell they continued with their tradition of seamanship and built a formidable navy by the time Emperor Tiber Septim came around, and despite having a huge imperial fleet -and skilled admiral- at the Battle of Hunding Bay, the Empire almost lost, if not for; A lucky poisoned arrow and a bloody dragon. 

It is worth to note on two occasions Tiber Septim needed a plot device to win. All of them sea battles. One was a Dragon and the other the Brass god.

However I think the Ra-gada and the Atlmer are skilled at sea for very different reasons obviously. For the Atlmer it would be their magic and maybe better then average ships, and the Redguards due to superior seamanship mixed with the battle prowess of their marines. As one on one fighting is much more prevalent at sea ship-to-ship engagements.