One thing to remember is that while there are rebel troopers, they're a very different variety.  For one, they know from the beginning that they're going to lose.  They know that they're mostly there as a holding action to shred papers, burn computer drives and buy time for others to escape.  As a result they are incredible vicious and determined.  Think about it.  These are people who have volunteered for a suicide mission!

Most of the time rebels are small guerrilla groups with whatever they feel comfortable with as weapons.  They rely upon stealth and cunning over brute firepower.