Assassins don’t have it very easy.
Warriors can go fight enemy after enemy and take very little damage in the process due to their higher armor and then they can just stand around for a short bit and regain most of their health.
Mages can fight tons of enemies, have long range attacks and don’t suffer from the problem that assassins do where if the enemy is close then you can’t hit them with your good attacks. They also regain MP very fast whether they stand still or not.