And what about special mercs such as docs, medics, scouts, drivers? Each of them could have unique statistics and abilities so they will be helpful in other ways than combat.
Doctor - high doc skill and ability to fix broken bones once every X minutes, not a field guy = medium small gun skill, low hp, 0 armor, can use FA to heal 60-90 hp every Y min (X>Y)
Medic - high FA, can heal 140-250 hp once every X min, if healing over max HP he can add +30hp over maximum for short period of time, better with gun than doctor
Scout - child of the desert, very high outdoorsman skill, ability to track animals (makes you choose what kind of creature you are after and you will encounter them more likely), better position when entering encounter
Driver - +X% travel speed while traveling by car and reduce fuel consumption
These mercs could have more types. Like amateur nurse/self-taught doctor/doctor ; medic/field medic ; tracer/scout/ranger ; driver/road warrior

. Each type with different pros and cons but generally self-taught doctor would be better than nurse and doctor would be better then self-taught doc.