I don’t think there is a better online Q/A system than Quora. But the problem I see is Quora forces, people, to join the community. After reading about two or three answers, you can’t go further unless you log in or join. I signed up at Wikipedia about 8 years ago to help other people get what they need, same as older Wikipedia contributors who gave me what I needed to know.
Quora forces people to join but doesn’t explain why I need or have to join this community. Curiosity is one of the reasons that attract people but it attracts them to a product they don’t know what is it not something they actually know and worse than that, they can’t trust.
What people get from Quora is not trustworthy most of the times and people know that and when you are forced to join a system that is maybe an alternative of another one, it makes people angry and disappointed.