You forgot that the avarage weapon dmg takes ap in acount, so its a lot more than that. A rogue with t2 weps has an avg MH dmg close to 2700.
So it goes like this:
Backstab would be: 2700*3,64+1634 = 11468 costing 40 energy --> damage per energy = 287
Hemo would come out to: 2700*2,25*1,4 = 8505 costing 29 energy --> damage per energy = 293
So, its more or less the same DPE. That means that, yes, hemo will be viable in pvp, where you can choose imp recup over puncturing wounds, and another glyph instead of Backstab.
Thank god hemo is back.