The 30% is based off the weapon damage, so you'd get 30% of 18- 20 which is about 5-6 which vs 80 resist is about 2.
On crit thats 70% of base damage so 12-14 ish and versus 70 resist thats about 3-4.
(Classic bonus was the same way giving a % of the weapon damage but pre AOS there wasnt exactly much damage absorbtion like the resist system in place now. so 30 % had a larger impact)