There are two topics about medics, and in both we can find some nice ideas. Hmm.. what about implenting obtainable profession-perk system, that will be like creating classes in other MMO's, but still not determining 'the-one-only-good-way'.
Gunner: +20% to weapon skills,
Medic +30 HP healed per FA use (and maybe with slight nerf FA for pure combat characters to make combat medics needed?)
some other classes like crafters, etcetera.
Still, if somebody want to make a hybrid character, i.e. bigguner with high doc/fa, he can, but having a medic in a team should be still more efficent. Maybe let medics have random % chance for reanimation (consuming super-stims and medkits) for killed characters not ripped/melted into parts/puddle?