Last night we swapped out a shadow for a gunslinger. Crazy that there is almost a 1k difference in dps. Yes there are other classes that can get close to 3k ds but they require way more work to achieve that compared to slinger/sniper.
A huge part of that is Orbital Strike on adds adding extra DPS on top of his single target damage. Only snipers and slingers have a Cast-it-and-leave-it AoE (orbital-flyby). Upside is it ticks for damage (on adds) while you go back to doing your single target DPS (on the boss). Downside is it stays in one place (orbital) and relies things to remain underneath it.