Pontus, you asked where the uncertainties begin. I'm happy you asked that. I love these "traditional" lines. I did graduate work in medieval history, so I spend most of my Geni time working on them and I'm always happy to have a chance to talk about my favorite subject ;)
For those of us with European ancestry, there are no reliable lines before about 600.
That means there are no proven descents from China, none from Genghis Khan, none from the Roman emperors, none from Mohammed, none from Jesus, none from Odin, none from Adam and Eve.
There are good lines back to Charlemagne, but we only really know maybe 18 of his ancestors. There are good lines back to the Irish, Welsh and Scandinavian kings, but they start to disintegrate about 600. Too much political tampering in later generations.
Many of these lines are part of our "cultural mythology". The lines can't be proven, but our ancestors believed them. That makes them a part of our collective history, I think. We should keep them around on Geni, but we should learn not to trust them.