Well, to take up my usual position as resident critical asshole, (if you'll pardon the language) it's not realistic to expect a civilian mining craft to be able to stand up to two fighting wings of military fighters for more than a second. On the other hand, it's highly realistic that if you're attacked, one of the first things to suffer is your nonmilitary logistics force. It's the way it is in real life and in any semi-reasonable RTS, Homeworld 2 included. In addition, having nigh-invincible miners makes commerce raiding almost impossible, whereas in the Star Wars canon universe, it's one of the main tactics of the Rebellion. I'd say that the miners are too well armoured and too quick to self-repair. No kind of vessel, no matter how highly automated, can go from nearly dead to full health in three seconds. That being said, it's not a major issue. I'd axe torpedo spheres first. But that's just me.