Don't listen to the bads. We do just fine endgame.
Sorcs can put out solid PvE damage in either a full lightning build or a full madness build. Pick one and learn the rotation. I parse at 1500 or better on every ops boss using madness. I like it a bit better than lightning because it is more mobile. You won't do as well single target as a Marauder, but in boss encounters with a lot of movement or multiple targets, a madness build can really shine.
I also like Madness because it works for PvP. Lightning doesn't. Ranked PvP is a bit screwy because of a couple of overtuned specs (Rage Marauders especially), but I do 300k-plus damage and 100k-plus heals in every warzone with my madness build.
What about full lightning doesn't work would you explain please?