You could add fix the team composition for missions… How many times we see 3 players of the same class? Too often.
I don’t play damnation but i agree with you about the contract system.
It should be something generic and that give you the shop currency while you progress on with a cap about what you can get by week for each item:
- Missions, more you do missions, more currency you get with a factor depending of the difficulty
- Mobs killed: more you kill more you get currency with a factor of:
- Melee gives more for zealot
- Ranged gives more for veteran
 
- Grim / scripture you carry on… With a bigger bonus for grims
- Monstruosities killed