Ok I'll go a litttle more in-depth
Wastrel's worry is 64 damage, lets say, for 5 energy. We are now looking at 13 damage per energy, yes?
However, you need to remember that only about 1/3 to 1/2 of these will actually trigger, because most mobs do use quite a few skills. The only way it can work well is if you shutdown a target, and focusing your arsenal on a single target is inefficient.
So now we are at, say, 6 damage per energy, on average. While certainly you'll achieve closer to the full 13 d/e on some enemies, you'll get even less on some. And that energy cost is going to add up, fast. Imho, thats a slot that could be used for something more efficient.
My primary damage source on my PvE mes is empathy. There is no downside of this skill. It costs 10 energy, lasts 20 seconds with 30 damage per hit at level 15. Assuming an enemy never stops attacking, you're looking at nearly five to six hundred damage, or 50-60 damage / energy, nearly ten times as efficient as wastrels. Granted im taking best case vs worst case, but even with reversed roles wastrel's doesn't compare, because empathy is fire-and-forget.
Combined with distortion, empathy means you can solo just about any physical mob, even in high-end areas. I have killed the groups of 2x impalers with distortion and empathy in FoW, because I can hex both and strafe with distort. Combined with my second favorite mesmer elite, and the mesmer king of triggered damage, Ineptitude, you can deal minor damage and blind a target. These combined mean you can shut down 1 melee enemy, and demolish a second. And empathy has a nice little 10s recharge, meaning you can spin around and empathy what you put ineptitude on. That's two melee mobs that are going to die.
On top of that, empathy triggers extra on skills like barrage. You can't hate a skill that deals up to 186 damage to a target at once (rare, but in FoW its not uncommon if the group is balled up).
Empathy also works well on casters... especially casters that don't self-heal. Most of my examples are from FoW (my area of specialization) and empathy rips the heart out of shadow memers as well as all the melee opponents.
Now, backfire. Backfire is not only for the damage, it also completely negates healing. A shadow monk's heal area will not heal anything on himself with backfire on, nor will his orison. That's essentially lockdown for 10 seconds, and bonus 140 damage if it tries to cast on something else. Backfire also devastates spamming mobs like Doubter's dryders, Mindblade spectres, etc... it's not as scintillating as empathy, but it gets my vote.
With those two skills, you have enough damage to rip apart most enemies. Other skills I like :
Shatter Hex: 15 energy for AoE 120 damage at 15 dom. Anet reduced damage from 140 to 120 in an old update, but decreased the recharge time to near-spammable. The best part? The recharge time is near-exactly how long you need to regen the high 15 energy cost. Hex removal + high damage to area? Sign me up.
Clumsiness : Interrupts enemy attack and deals damage. Decently fast recharge. Go figure.
Ineptitude : The king of PvE illusion spells. 10s blindness on a target, a blocked attack, and damage. When a melee mob rushes you, THIS makes the problem gone.
Moving on!
Why do I like distortion?
Because in PuGs especially, warriors tend to lose the aggro. With distortion + Ineptitude + Empathy, you can kill just about any melee mob in FoW, and almost all anywhere else. I've brought down a Bladed aatxe with just those 3 skills. Luck, but the principle stands from that - empathy is potential collosal damage. It needs someone to be hit for it to trigger. If aggro is broken, that person should be you. Preferable using distortion to avoid conditions like deep wound.
Though, to my credit, I never said any of those are bad, and I did have Empathy and Backfire in the build I suggested. 
