You are not losing ONLY the 15% PVE dmg, you also lost the % of SS, and the % of Gr. Ruby on SS.
For example, if you have a +21 Limited Bow (3252 p.attack) and a Greater Ruby lvl2, you lose 15%+14% (from the SS) +20% (From the Ruby) = 49% PVE Attack.
So 3252 + 49% = 4845 P.attack. Compared with the P.attack of a DW, 4225 is much better....
Espessially if you think that DW cost 1,7T......