That isnt how math works...
First a maxed inquisitive had 16 law dice, not 12 so it is a 12.5% loss of law dice/damage
The scaling of attack power is a 25% loss to the law damage
those are not additive, those are multiplicative. For simplicity lets say you had exactly 100 attack power. Your law dice average 4.5 on the roll, multiplied by 3 to get 13.5 damage on average per die so 16 dice is 216 damage per shot. Losing two dice lowers that to 189 damage per shot. The attack power change takes it from a times three to a times 2.5 so 11.25 per die average, with 14 dice that is 157.5 damage on average per shot. So the change is from 216 per shot to 157.5. A 27% damage loss to law dice damage on non-lawful targets
Law damage was maybe 25%-30% of my damage at 30. Lets way it was 30%, so the changes to law on your side represent about an 8% loss of overall damage
The double shot and rapid reload charges are the more significant damage losses as most damage is from the main shot, not the law on your side dice. My inquisitive I just reincarnated had 89% double shot at 30. I only had two primal reincarnates, so was getting 6% instead of 9% from that and didnt have any gear for stacking double shot, just had a base Sharn double shot item and wearing the Sharn ranged set. Many people will have less and some will have more than. So lets use 85% as something fairly easy to obtain for an average player with gear, feats and enhancements. Getting half per attack is a 23% damage loss at level 30 as you just flat out lose 23% of your attacks, that is extremely significant!
but the point is no, it isnt a 70.4 % loss, as math doesnt work the way you are using it
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it is a big loss, guessing with the attack speed changes they were shooting for around 30% reduction in damage(not counting the loss from IPS which is very hard to estimate)