All of that is a given. I'd say they've done pretty well so far.
Fact is you have nothing on the Thalmor. Burden of proof is really on the Empire now, who has half a chance to put down a petty rebellion. So far it doesn't look good.
Empire nearly put down the petty rebellion, Tullius using limited resources, manpower and working against Thalmor interference nearly destroyed your little plans. All within a few short months.
I find it quite amusing you would use an argument so many Stormcloaks try and pull, "can't end a little rebellion" despite the fact it actually took an immortal aspect of a God to stop the Imperials from winning, I'd say it is looking damn good.
Thalmor had one thing going for them, element of surprise. They blew it.
Thalmor only rose to power when the Empire was distracted during the aftermath of the Oblivion Crisis, they only managed to expand when the Empire had descended into Civil War during the Stormcrown Interregnum. Managing to cause a coup in Valenwood while Mede was dealing with recovering the Empire from the Stormcrown Interregnum and what effects of the Oblivion Crisis that remained.
Had it not been for a floating island of doom, and hordes of undead sweeping across Cyrodiil. The Thalmor would have been annihilated long ago. Fact is whatever espionage the Thalmor have been doing isn't working against the Empire, they couldn't even figure out the strength of the Imperial Army when they've had over one hundred years of plotting, and preparing.
They were arrogant and foolish enough to actually believe Titus Mede II was going to surrender in the winter of 174-175. Clearly they have no understanding of mankind.
Thalmor have quelled most of their disorderlies, (including the blades) the Justiciars are always combating terrorism.
Please, the Thalmor couldn't even handle Delphine. The entire success of the Thalmor has been due to the fact the Empire has been distracted or was content with their current holdings.
Now the Empire's focus has turned towards the Thalmor, gearing up for war. You really think they're going to defeat the Empire in a war they're prepared for? Dominion couldn't even defeat a weakened unprepared Empire, now suddenly they can beat the Legion fighting on their own terms?
The Thalmor of the Fourth Era are an empty boast, a corrupted shell of those who came before. Not even worthy of taking the name of Thalmor or the Aldmeri Dominion.