Mages are great - I'm not knocking mages. However, in order to do any real DPS mages need to plant and shoot. A huge chunk of the warlock's DPS comes from things you only have to worry about every 18 seconds or so - and Pets are kinda fire-and-forget.

When I play my mage solo, even with horrible gear I can get pretty respectable DPS. However, my locks were doing more DPS at 70 then my mages are at 80.

Fun note - downed my first Heroic Boss on my new team last night!