Is the question, how hard should one work to complete a Master's Econ degree? If you're looking for an easier route, why not take good programmes from Edinburgh (SGPE), Warwick or Erasmus? As far as I understand UCL is not an outlier and Cambridge MSc Eco is a seven day week too.
Regards to work, If you seek a great think tank role / original research capability surely you would need to apply yourself to achieve the highest scores, and signal a willingness to perform in role. Would government economics offer a more generous work-life balance that you hint at?