30% is still correct, but its only applied to the base damage of the weapon. So if the base damage is 15, you only get 4 additional base damage out of it.
More so, while that in theory is fine, the reality is that if you want LJ on your template to maximize damage you are forced to cough up something that is probably more useful all around. There are certainly ways around it through suit mods and personal preferences.
In my case:
120 Swords (can use axe)
110 Bushido
110 Parry
120 Tactics
100 Anat
90 Healing
70 Chiv
Id have to forego healing most likely in this scenario and rely on a darkwood suit and chiv heals and life leech weapons to keep me alive in order to add lumberjacking. Bushido w/ LS offers far more damage and other abilities (healing/CS), as does chivalry (EOO/CW/Heal/Cure/Travel).