I was full madness spec while leveling, but never had any problems unless there was MORE THAN 2 equal level elites and 2 regular mobs. In other words a H4 area was usually too much, but only rarely had problems with H2's. And my Khem was usually in crappy gear.
Just make sure to use your whirlwind and then send Khem in. Take AoE's off his toolbar so he doesn't break mez. Keep him bubble him before a fight and heal him when he gets about half dead ish. Other than that just throw out as much damage as you can. Took me some getting used to, but once you figure out where to put your deathfield to hit the targets you want and not pull extras or break mez you will be way ahead of the game.
I had absolutely no problem with single targets this way either and was soloing every single named elite or champion I could find. There were several H4's that you could do just the objectives and then fight a solo champion at the end. I could solo those on my sorc. No other classes that I have tried have come close to that yet.
You are talking about a low level PVE environment which is completely irrelevant. We are talking about endgame PVP balancing and fundamental sorcerer problems at level 50. Just because you had success in lowbie heroic quests does not mean the class is functioning properly in pvp or raiding endgame pve for that matter. Pay attention to the context.