your whipe is definitely better,even if you get that legendary to +10,it will have less or equal DPS overall,for now i believe 10% critical is best for you,till it starts getting normalized after you get planegate gear :x
I can only confirm to you that there won't be much of a difference ( if not weaker ) from changing to that weapon,it will also cost you to +10 it,so,maybe not worth it?
Also,that's common now,finishing area 4's scenario would generally end up on some boss droping a legendary Lv50 weap for you.
Well, the wand has 13% back critical, so if you manage to hit back at least 80% of the time, it's worth it :v
Edit: The reason I say this is because CDR is more OP than crit
I'd use the whip. But if you get the Plane Gate legendary staff, definitely switch to that. It has 12% Magical Critical Hit Rate when fully upgraded so you wouldn't even be losing out on Crit.