Actually your attack will bc of the 75 str that the blade gives, which gives you an additional 75 attack. But the OP wasn't asking about attack he was asking y he isn't seeing more dmg.go to your stats page
on the right hand side of the screen (under your xp bar; to the right of your stats)
you will see five thingies:
Hp
Energy
Attack
Damage
Defense
and maybe something else
your attack will not increase if you equip your golden blade
your damage will increase though probably about 240 or 230 or something depending on how high your strength already is (the higher your strength already is the lower itll be)
To OP:
If you unequipped your flint sabre in your mainhand in order to equip your OFFHAND blade and then u see that your dmg is the same as when you didn't have blade... Put your main hand sabre back on and your dmg shall skyrocket.