I have tested 8-gates with and without Injury stat (Inferno) of +240 using my Susano Sasuke fixed Critical Chase or GNW Ten2 on damage range below 10,000 (The higher the damage, the higher the range, so avoid doing more than 10,000 damage, my sample is around 6000). I also made sure it is in the same 'MOVE' position, and only replaced non-causing damage gates such as quick.
My result have shown that with or without that 8-gates, the range remain the same, and the average are more or less below 200 damage, even proving that without Injury, the average damage could be higher.
I have also heard my other group mates doing similar tests to get similar results.