Proof of brain is much better than just a website where you ask questions. Here you may improve yourself motivated by earning rewards yourself and rewarding others for their knowledge. I think quora is centralized and they may remove your content and your account any time they like. They even have moderators telling you what to do and what to not do. But here our content will stay forever and noone will be able to delete your account. The only thing we have to fight the abuse is to mute, downvote, and ignore people who want to abuse the platform. That's why it's much better. ☺