So no the Altmer are the ones who truly lost the war imo. Its fairly evident that they aren't as powerful as they were in the Great war when they were expelled from Hammerfell. The invalids being left in Hammerfell from my point of view was a way to tell us that the Imperial General gave the Redguard under his command the chance to stay and fight for their homeland. And to be fair many of the warriors of Tamriel are current legion or ex legion. So saying the legion saved Hammerfell is only a half truth. Also the 5 year war had no Imperial aid at all, yet Hammerfell still fought the Dominion to a stand still. Its not like the Dominion couldn't ferry in more warriors, being that the island is pretty much right next to Hammerfell.
So for the past 25 years the Dominion has been trying to weaken the Empire by showing dissent among the Provinces. So when they finally do have the numbers again, the Empire wont have the Nords to bail them out again.
I wonder how large the two Dominion armies were, so we could get a proper head count on their dead. Do we know the actual number of Imperial Legions? Because with 3 legions destroyed and assuming they are built like Roman legions that's a confirmed 15,000 dead Imperial soldiers. I'm guessing there was probably 10 or 12 legions before the war and with that, that's around 37,500 dead Imperial soldiers. This is also without the Imperial and Redguard civilian deaths. So about as many Imperial soldiers died in this war as some countries had in the second world war. Sadly we don't have population of the Provinces.
As cold as this is about to sound I think the Humans could afford this more easily than the Elves could. A lot more people would of died before this war ended but in the long term the Humans would of out lasted the Dominion. Two of the Imperial Provinces were willing to pay this price, Skyrim and Hammerfell. The two martial nations in the Empire were willing to continue the war and yet the Empire let one go and is about to lose the second.
The future of Tamriel is going to become interesting if the Empire falls
PS I still maintain the Nords are more than capable of defending themselves from the Dominion



