I gave this topic some more thought, and realized that many of the claims here have been incorrect. I don't know if it is because of ignorance or exaggeration, but some people have overstated the efficiency of repeatable quests. I would like to explain exactly how much effort it does take to earn medals this way.
The first thing you need to know is that diamonds and medals are not in fact possible prizes from repeatable quests. There is one possible prize, which produces medals exactly once and then produces only medals. The probability of getting that prize is about 1/15. This means that earning 155 medals requires 31 medal rewards and one diamond reward, which means about 480 quests total.
The second thing you need to know is that you don't need to train just one spearman and slinger for each quest. You need two of each. The quest is in fact to build four of each, but you can already have two ready before accepting the quest. If you have three or more ready of either, the quest is not offered at all. This means it is impossible to repeat the quest every two minutes, since it would require 60 slinger ranges. If you have 18 slinger ranges you can repeat the quest about once every 7 minutes.
The conclusion is that getting 155 medals requires about 480 * 7 minutes of work, or about 56 hours. Given just five days that is an incredible effort, and there is no way I will believe any bronze age fighters spent more.