Melee damage

[Bigfish]

My fire mage rotation is Combustion, Scorch, Pyroblast, Fireball, Scorch, Fireball, Fireball, Fireblast

My arcane mage rotation is Arcane Barrage, Arcane Missiles, Arcane Blast, Arcane Barrage, Arcane Missiles

My destruction warlock rotation is Curse of Agony, Corruption, Immolate, Incinerate, Incinerate, Shadow Bolt, Chaos Bolt

Ok, in that case, looks like your /castsequences are to blame. Pyroblast can really eat up your DPS, especially since a portion of its damage is a DoT. I don't know enough about Arcane Mage rotations to comment there, but your lock is going to see reduced DPS simply by merit of it taking ~6 seconds for a Direct Damage spell to hit, and chances are your dots aren't ticking off on mobs long enough to do the damage they are supposed to. Curse of Agony in particular is back-end loaded.

That said, instance DPS isn't necesarily an accurate portrayal of your ideal DPS. Many spell rotations are idealized for extended, single target fights. The important thing is you are clearing content. If you are clearing the stuff you want, I wouldn't sweat the individual's burden.

If you want a second look at your DPS, I'd suggest a training dummy in a capital. You will get much different numbers than you get in instances, ideally more in line with what you expect.

All else fails, run your characters as individuals with a PuG or something, and try to act like your alts do. Ideally you'll get a firsthand look at what is happening to each character specifically.