Sustained dmg is the main reason of this class (and many mages) if you nerf that then you might need to push its burst and balance would need to start again.
You really think, the balance is over like it is right now? If so you are completly lost. Or didnt played much at all.
For sure its not only mdps who is still OP. If we take a look into Chain of Arcadia we still see, Champ/Wl still overperforming or a Wr/Rouge or a Wr/Druid... i can continue so long. But also many mdps classes disgusting. Sure you need try compare in same runs with same supp etc. Which is actually pretty hard. But still it is.
And we got so long now no balance patches, which makes me kinda sad tbh.(i dont count last one, cuz it was more or less bugfix) Couse, like Merkur said. So less Leather Dps who perfome atleast well or even with some broken, chain or mage classes. (actually just r/ch, when he play nearly perfect)
For my opinion her is still much work needed to make it fair for each "dps" class. And then we didnt started to talk about tank classes or heal... x)
Greetings
Côsmô