March 18, 2014 6:40 PM EDT
I think what's been proven is that the only way to beat the Aldmeri Dominion (In open combat) is to fight them on a turf of your choosing that you are familiar with. Think about it, if Hammerfell's geography was like Cyrodiil's, do you really think the Redguards would have beaten them? The only way to beat them would be to lure them into Black Marsh (which is kind of impossible because the Argonia have cut ties with the empire), or Hammerfell, but I think the Elves will be more than hesitant to go back there. Also, good luck getting the Redguards to cooperate after the Great War.
That being said, the Thalmor aren't unbeatable. The best ways to beat them would be to:
a) Take the initiative. Don't wait for them to attack Cyrodiil; attack the Isles directly! They'd be forced to return troops there, and perhaps other lands could be taken back. Think about it, the land area of the Aldmeri Dominion is tiny compared to the Empires' (counting Skyrim). We've never seen Empire vs. Dominion where the Empire was ready, per se, for the war. The next war would be of the Empires' choosing, not a hurried defense against a prepared, ruthless enemy. Granted, the empire is much weaker now and may not be able to win, which brings me to the next option.
b) The most interesting option - Stage a coup in Valenwood/Elsweyr. Give the Thalmor a taste of their own medicine. The Bosmer hate the Thalmor, through lore we can see they're treated as second class slaves. Instigate the race, and you could gain a VERY powerful ally in the Bosmer. Elsweyr would be harder, but the entire alliance is based on the Thalmor "returning the moons", which was a ruse anyway. Get rid of that, and the Cats don't really have a reason to stay allies. Besides, Cats like shiny things, let's bribe them ;)
That's my 2 cents. Sorry about the "HOLY WALL OF TEXT".