Even if you have so-called anti-cap loadout in GS (2xPulse, 2xGB Razor front firing) you are in still a heap of trouble against other GBs.
Even though the GS is small and quite maneuverable there is no way the other guy is that bad a shot for the whole duration of the fight that it takes the GS to chip away the other GB.
Basically if the other GB knows anything at all he'll force the GS to jousting and that's it. Game over. And avoiding the jousting is practically impossible since the GS lacks the speed superiority to stay on the other GB's six. Even more now because all the other transports/GBs got their thruster speed upped to 150 and GS is still 140. (I've reported that and hopefully it will be fixed on the next update).
Let me be clear about this. Most people think that GS is as agile as a bomber. And they cry, it's a killing machine impossible to hit. No it is not. In agility it's somewhere between the bomber and other GBs. It sure feels like a slug on tar when you try to bring her around (very subjective opinion), but that's because I've gotten used to flying bombers and fighters.
This is probably going to be shooting on my own foot, but if you attack the GS perpendicular to it you are doing it right. A) Target is the biggest possible and B) GS can ony fire 2 guns at you.
And about it's supposed role. Anti-fighter/bomber. It really does fill that role very well. If I had to go against one I'd say that I'd think chances for 2 fighters/bombers to win it are not that great. Personally I'd prefer 3vs1 odds.
I can't think of any cases where any complaint about the GS have any merit. It's very strong against the smaller ships due to it's size and maneuverability, but it can only really support 2 missile turrets (which is ok). So maybe using GS to go after a single fighter/bomber is considered bad sportmanship, but I think a fighter/bomber can easily escape it by thrusting. It's only fighter's own fault really if he sticks around. And it's definitely weak against any GB/Cap.
And it's not the most useful ship either in fighter furballs, because the GBs are always the ones to go first so the volume of fire will finish the GS off.
Only then if there are 2 or more GS working together it becomes useful.