As affliction your main job is actually the immense pressure you can put on the other team with multidotting 3 targets. Not so much finishing off. Though you do have Drain Soul as a very nice execute for that and it works through pillars
Make sure to have their healer on focus and spell lock/lolcoil or catch him and the other guy in a howl of terror and then Drain Soul on the main target who is below 25% for a quick kill.
Destruction is another playstyle and works good for single targets, but is easily gimped by dispels/interrupts.