Every difference of 100 injury stat between ninja A and ninja B increases the damage landed by ninja A on ninja B by 1% on a critical hit. This means, since kushina hanabero hits 3 targets with her mystery that the damage she lands on the 3 targets is not the same and if she is quite high stacked in injury means that may literally nuke move 3-4 ninjas. A 7000 injury difference could indeed justify that level of damage considering the basic damage itself depends on rng and rng factor goes up to ±25%.

2011*2*1.7*rand(0.75, 1.25) = 5128 - 8546. This is the range of damage you could suffer with a basic damage of 2011 and a difference in injury stat of 7000. 8060 is in that range.