Have you tried it in co-op?
In Mercs 2 the missions are identical in co-op, meaning you get twice the firepower and firing arcs brought to bear on the same number of bad guys.
...Actually I guess there are a couple mission types where they double the resistance, because co-op "transport" missions gives each of you a truck full of wobbly-physics-objects to get to Point B, and when the enemies show up on screen, they are sometimes conjoined-twinned together. (Pandemic's QA must be ineffectively used.)