My arguments against the Empire are in red.
Your evidence for 1?
2. The empire banned slavery. Slavery was continued in Morrowind because the treaty that brought the dunmer into the empire allowed the Dunmer to continue their old traditions. The rest of the empire was disgusted and frustrated by that.
3. Evidence?
4. Likewise, see no advantage/disadvantage to the Thalmor at all.
5. Your last point is entirely invalid, as you don't understand the ways that the guilds work. The head of the mages guild was the one that outlawed necromancy. The guilds do not enforce laws - they don't have any right to. They are there to provide services to the public. In particular, the mages guild is there to centralise the study of magic, so that greater understanding can be achieved.
Both times that Necromancy was banned outright in the guilds history was when the number of necromancers in Tamriel were under the leadership of Mannimarco, King of Worms. And Mannimarco is the one that attacked the mages guild. I don't know of a single Lich in the game that is actually "white", all of them are most definitely "black" and evil. Mages guild is entirely justified.
Also: Empire wasn't a dictatorship. No difference between the Empire and the modern USA. In fact, the empire is even better than the USA - it has one central authority, not all of the state authorities making conflicting laws with one another.
Skyrim did have a king. It was his death that sparked the civil war.