I think my biggest problem is the empire is playing the long game. Thalmor excel at long game strategies. They waited 150 years to make their move, and they did it nearly flawlessly.(Faulty info from a hammerfell agent was what screwed them over in the war) The empire should not have survived. Decianus unwittingly saved the empire when he left "invalids" in hammerfell. The Thalmor have been gathering intel and subterfuging for 30 years again now. The empire has 1 less province to count on. It's only advantage is that it is expecting an attack. But the Thalmor already know this and their current troop count and deployments. They also appear to be bribing some of the officials in the high council. Getting this war going again is going to be a political mess.
Ulfric wants to start the fighting ASAP. Don't give the thalmor a chance to plan. Don't allow them time to gather intel. Keep hitting them until they break. The thalmor are terrible at the short game.
Yep, blame that long Elven life span, problem is the Thalmor have had a chance to plan, they waited a 150 years of it as you said, and probably been planning a lot longer, and apparently they got enough troops to spare for there things like Talos worshipper hunting. The've hunted down and killed all but two members of the blades that you know of.
And they signed a peace "treaty" with the Empire that pretty much gives them everything they want, including allowing their agents to operate within imperial borders without repercussions. That's not a treaty thats a conditional surrender.
But as bad as things are for the empire, and independent Skyrim would be worse, especially if Ulfric is planning to immediately lunch a suicidal assult on the Altmer's home island and waste whatever troops he has left after this long and bloody civil war. I think I read somewhere that it's a bad idea to mount an attack unless you overnumber the defensive forces 2 to 1. Not to mention the Altmer are very good at making things go boom. Which makes things all the more harder if you can take out 10 charging nord warriors with a single fireball spell.
Here's what I'm thinking, if Bethesda hasn't thought of this already, make the move as Dovahkin to become the next emporer, rebuild the blades and restore a dragonborn line to the throne. You're that wild element that the Thalmor didn't acticipate, use it. The Empire, as you and some others have mentioned is on its last legs, but you could restore it. Which is all the more reason to join the Imperial cause, it would be far easier and less bloodier to do all this if your seen as a hero of the empire then the hero of a renegade province.