I agree with you. A domain filter would be the best as there are other sites in addition to Quora that provides junk content.
For example, for all health type of search theres a website named healthline.com which appears with 2-3 of the top results. I wish I could block it somehow.
This used to be a feature of Google search. They removed it and published a Chrome add-on that does the same, client-side. I have switched back to Firefox and there are similar add-ons there too.