Hi
I don't have any answers for you but it is a very interesting question you pose. There are different ways people approach genealogy. Some like to 'collect' as many people in their tree as possible and this includes, as you've found, tenuous links to many weird and wonderful, and often fictitious, historical figures. Other people are more interested in the social history of their family over the past few hundred years and concentrate on finding out about their lives. Personally, I think when you go so far back it can become meaningless. How you interpret your links to Zeus or Noah does to an extent depends on your belief system. For example, the head of the 'family tree' for English kings is God. The kings power is divine and so a link had to be created between the two in order to justify and maintain the right to rule. For me it's a convenient way of maintaining the power of the church and state and keeping people in line. Sorry, I don't have any answers for you.
Regards
Julie