The way I see it is that Justicars seem to take their oaths later in life, meaning that Justicars (like Samara)could have had military training prior to becoming Justicars, meaning they likely spent time either as Asari Marines, or Commando units if they were skilled. This would give them experience that would assist them in their time as Justicars.
In this regard a Justicar would be like a particularly powerful and experienced commando that for whatever reason took an oath as an enforcer of Asari law. They get training as a Justicar but that is in addition to their prior training and time as a commando.
On a kinda unrelated note I think Tela Vasir ( The Vanguard Asari spectre from Lair of the Shadow broker) is a good example of a powerful Asari Commando type that went on to something else,in this case being a spectre. She is a fair deal more competent than the commandos you stomp in droves fro the rest of the game, but still (probably, since I don't know for sure she did) was/is an asari commando.
going in another random direction I think Calling the class Commando fits better since it describes a broad range of skill levels, where as a Justicar seems to require more experience and training in order to be able to pursue and apprehend violators of Asari Law. And while I'm sure that Justicars ARE taking part in the conflict SOMEWHERE, It seems like they'd have their own tasks to do rather than the missions present in me3's multiplayer.
What sorts of missions would you give to Samara during wartime? *shrug*
Just my random thoughts on the issue. XD
erm. TLDR: go back and read it lazy monkey. Just call the class Commando and be done with it.