In terms of Weaponskill Damage Perdu is not that impressive and wont put out as big numbers as other higher Damaging scythes.
What really makes this Scythe shine is the low Delay 6-Hit Drk/Sam(Same Delay as Naglering) which puts out a very nice DoT over other scythes. Faster Weaponskills = More Damage over Time.
Is this the best Scythe? Short Answer: No.
Drk unfortunatley doesnt have One OMG WTF Amazing weapon like Sams have their Hagun, or Dragoons with their Vforks.
Properly Geared other Scythes can and WILL outdo Perdu. In the end its all preference, playstyle and how you gear yourself.
This is still an amazing scythe, but other Scythes such as Tredecim should not be underestimated by any Means~
DMG is not a large factor when comparing high level Scythes, since it becomes increasingly less significant as base damage becomes higher.
An increase of 1DMG on a 30DMG Dagger is 1/30; an increase of 1DMG on a 93DMG Scythe is 1/93: significantly smaller. During WS, your WSC term will be adding to this, making the increase even smaller still.
Perdu is powerful because of its delay, firstly: this is enough to beat Tredecim/Death NQ without any further input. Secondly, accuracy+5 which can be used either to make you suck less, possibly eat Red Curry, or use Blitz Ring etc.
Finally, the Attack maintains its value more or less and so can actually be better than the higher DMG in a hit-for-hit basis anyway.
Basically, Perdu is the best nonrelic Scythe in most situations.