More unique skill it's a step in good way. Please consider also adding some randomness to the fight.
Now the fights are soooo boring because you just do the math using the simulator and there is only one 100% sure winning strategy - buy 1000 bouncer/rowdy (yes, the cheapest units) more than your enemy has total number of units.
It reminds me situations from the Civilization (PC game) when spearman (unit from ancient ages) could won with a tank (unit from XXI century). Sadly in drug wars it works in the same way when - 10 guys with a baseball bat (rowdy) wins easily with a skilled guy with a machine gun (mercenary)
RE: Battle system: Implementing a unique skill for every unit