He's a violent sociopath who would willingly and gleefully set all of Skyrim ablaze so long as it's his flag flying over the ashes.

Do you have anything that actually supports this? Because if you just talk to the man and listen to his speeches they make it quite clear that he cares about Skyrim, its traditions and its people.

He doesn't care about the ban on Talos worship -- a ban that was all but ignored by both the Empire and the Thalmor until he started moaning about it. He doesn't care about the people of Skyrim being kidnapped and tortured by the Thalmor -- he holds sole responsibility for the Justicar presence in Skyrim.

The one that holds responsibility for the Thalmor presence in Skyrim and the Empire is Titus Mede II and the rest of the faithless imperials. Ulfric freed Markarth from the Forsworn and all he asked for was the right for him and his men to worship Talos, which the Empire agreed to. Only to take it back and imprison Ulfric some time later. Besides what man hides in the shadows to worship his God, only spineless imperials would do that.

He doesn't care about the Empire being "weak" or "toadys of the Dominion" -- any idiot can see that the Great War is far from over, and is merely on hold.

Of course he cares about that. He fought and bled for the Empire in the great war. Only to have it turn its back on Skyrim and its traditions. The Empire is weak and is dancing by the Thalmors strings. While the Empire let Thalmor agents roam its lands the Thalmor are free to find, study and destroy the Towers. Thus furthering their goals of destroying Nirn. After winning the war Ulfric makes it quite clear that he'll be taking tha fight to the Thalmor once Skyrim is restored.