Actually....at WoE, with F.B., thara and ray, the damage should be cut to 28.8%. Outside WoE it is 48%, that all is compared agaisnt PvM damage (on DH medium neutral, Vanberk for example).
Tried out RODE calc, geared in in ninja as good as possible to my knowledge (With TG, but no more miniboss/MvP cards) and put on a lot of mods, and against Vanberk, in calc the FS damage was 32536. WoE damage then should be about 9k max with all reduces (DEF counts, and Vanberks have low), PvP 15k. So...if he oneshots you at WoE, something is wrong.
If you are interested, this is how I geared him:
F.B
Odin Blessing-Tao Gunka
Vali
Vidar
Evil wing ears
Valk shield-Thara
2x necklace-spore cards
+10 MG, tri bloody boned
buffs and effects: lvl10 bless agi, +5 str +3 vit food, Aloevera, Magnum Break (marine sphere card), box of resentment. Final stats: STR 120, VIT 115, rest irrelevant, max hp 18339.
I can't think of anything that would seriously improve FS to point that it would oneshot anyone. Even +10 food won't get it more than few hundred points of damage against players.