I believe its because they have 8 Damage.
If you have Timber ( 2 Damage for all your cards) and use Fury, you can kill the oter player in one move.
If you have general and one other La Junta you will do 12 damage with fury...
We banned them because they have ultra good stats and very good ability/bonuses (stop power opp, stop bonus opp),
wich make them almost unstoppable.