Boomkins do a crap ton of damage. Starsurge is one of the many burst spells that you may be searching for, judging by your post. While druids also have other added advantages, being able to do a significant amount of damage in cat form as well, and being able to soak a lot of damage in bear form, not to mention the mobility of a druid. Basically, a jack of all trades.
Destruction Warlocks may also be what you are looking for. They play a lot like a back-lining turret, pumping away with those HUGE Chaos Bolt crits. Warlocks do have their downsides though.
Arcane Mage can build up some serious damage as well. Unlike the previous classes, it's not necessarily on-demand damage, and at times, it can be more difficult to pull off. However, you will have a lot of utility as a mage with your Counter Spell and Polymorph etc.
Hunter would also be an ideal choice. While Marksman has Aimed Shot, which is one of the mechanics you desire, I would recommend going for Survival. You will still do a lot (should be more overall) damage. It may not seems as bursty, but once that Flintlocke's proc, you become a killing machine - by definition.
Those are the recommendations I have at the top of my head, considering what you're looking for in your post.
