Lusos fight more or less like the Romans, but with spears and decent cavalry. Multiple lines of well armoured javelin throwing infantry can take on anyone head to head. You really shouldnt need to use skirmisher stacks to weaken the enemy. If you get into trouble then try and fight a couple of battles in the woods. Their advantage is 1) ability to hide and 2) much higher morale. That advantage does not directly effect attack capacity - especially with missiles. Just get the enemy to run then hunt them down.