This doesn't correspond to here, but yes Shivans weapons aren't really worth compared to Terran and Vasudan ones...
However in Inferno, there is an exclusive Shivan weapon, called "Swarm of Death", is an Harpoon (Aspect seeker) that Spawn around 14 Missiles when it explodes, if an Harpoon is deadly in FS2, then imagine what it can do when it spawn 14 sub-munnittions, even if 10 times weaker that the 1st Missile, it can do a lot more of damage......
When I add the support for players to be allowed to use Shivan ships, I really noticed, that probabily no one will choose them, the ships were unbalanced, I do multiple things in order to brough balance, but still there should be needed a few more...............
The only Shivan adventage is Slide acceleration (if there would be a key to use, I could evade everything...there is?) and Backwards acceleration...........
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But talking about FS2, I really like to use the Nephilim, it's a Mobile Fortress, it's shield are really powerful, carries lot of Weapons, and it has 7 Gun FirePoints, it may not have AfterBurner, but if someone would do a face-to-face challenge, I am sure the Nephilim would have the higher changes of survive