I think this whole genius thing is misunderstood. Someone can be a genius in one area and a complete DUnce in other areas. A lot of it depends on where your interests are. For example, I am totally fascinated by history and think I have a good grasp on it although everytime I really think that I find out much more that I don't know. OTOH, I have NO musical ability. My Mom even had me take guitar lessons when I was a kid but I have NO musical ability whatsoever. I see this a lot.
This is true of everyone to greater or lesser degree. My math skills are pretty good and, like you, history (American...especially the Civil War and 'Wild' West) is a favorite of mine. OTOH there are other facts of life I'd be better off leaving alone. Don't ask me to pull an engine block or go fishing.
The big difference though, is that a strong part of our knowledge has been developed by involvement and being successful in things we enjoy doing. To many of these DU'ers, they've never crossed into the realm of making their interests pay. They expect the government to provide what they're 'entitled' to. When they don't get what they want it's someone else's fault.