When you actually meet him in the DB questline, he basically just says that you're an assassin, he's an Emperor, and that it's his time to die. Then he just turns around and asks you to make it quick if you don't mind. I don't think a weak leader would face his death in such a calm manner.
In fact, there's a book about the DB on his desk when you meet him, which would imply that he only realized he was going to get assassinated soon quite recently. He has a remarkably calm exterior for a supposedly weak-willed person.
I disagree, simply because that it doesn't necessarily imply strong leadership. If he was a weak or bad leader and realized it, the same thing could have happened.
Edited:
I had a thought... wouldn't it be possible to make a game with all of Tamriel, even with modern tech? When you're in one province, the others would just be LOD models of the actual province, and they would be linked up in certain transfer areas, like a small Imperial outpost or something that would have a gate that would transport you to the next area. Then the area you were just in would be shown as an LOD model of itself. So in short, the entire continent wouldn't be rendered all at the same time, but it would include all of the individual areas. Size wouldn't be much of an issue, since skyrim itself is just 6 gigs of HD space.
The issue isn't the space, it's design. It takes long enough to just create a single city. Think of how long it would take to construct a full continent.