This isn't a challenge by the way. I have just been debating for a long time whether I should join the Imperials or stormcloaks and right now I'm leaning toward stormcloaks due to a few reasons that I was hoping someone could argue. (I might be straight out wrong about some things)
1. The Treaty has lasted around 30 years now. While it was to cease the conflict TEMPORARILY, 30 years is a long time for human races. If worshiping Talos is their way of life the Empire has taken a majority of it.
2. Poor politics in the Empire. The Empire failed to realize how accepting such a treaty would be even more harmful for them. Because of the treaty that the Thalmor had planned all along, Imperials lost Hammerfell and a civil war was started in Skyrim.
3. In the end the other provinces are second in interest to Cyrodil. For example, the Empire completely abandoned Morrowind in a time of struggle, leaving them to their doom. Morrowind depended on the structure of the Empire to govern them but the Empire had left when troubles came. Same thing with how the Empire was willing to give away a part of Hammerfell in the treaty. My point is, I believe the nations should have their own governing bodies and be in control of themselves so the provinces will fight for their own interests. The Empire seems to only use these provinces to their advantages and lack the heart that a governing body like the Stormcloaks can provide.
4. The Empire is holding Skyrim back. Whether or not Ulfric was right in creating more violence, the Empire is already crumbling. They are a fraction of what they once were. I don't believe they have the power to be able to fight for Skyrim and the other provinces. I believe the Stormcloaks have the heart and passion Skyrim needs to survive the Thalmor. In my opinion an alliance between nations can serve more useful than an Empire trying to work in different provinces at once. I believe an alliance with the Nords and the Redguards (and maybe even High Rock as I read Ulfric had tried to create an alliance with them) can prove a greater threat to the Thalmor than the Empire would at this point.