the problem is that of many quick firing guns. - in theory, they are equally efficient or even a bit more than the slower guns. - in reality however - it is easier to inflict an equal amount of damage with a 2.0 high damage gun instead of a 8.33 low damage gun.
so lets say - your 2.0 gun does 1000 damage - meaning you need to hit the enemy once to do 1k dam. - your 8.33 gun does 200 damage. - you need to hit your target at least 5 times to do the same amount of damage.
that means - you need to keep your target focussed longer than with the instant damage gun. - which in turn means you can start to activly dodge earlier.
reavers also "feel" like they use more energy for the damage they really do, which is of course a side effect of that you need to hit more often to do the same damage, - calculating the missed shots - you end up with a gun that does less damage for more energy.
all that comes down to the fact that - when you apply a linear give and take to a gun - a 1.0 gun doing 2k damage is much better than a 20.00 gun doing 100 damage ( in most cases )