humans allready work together as much as could hope to in public games.
my suggestion is to give the medkit-user a boost of speed or something, if used above 100 hp, so it would work like the stimpack in starcraft.
(without faster firing rate and health loss.
as for encouraging teamwork in public games: there are alotta retards i r eally would rather have solo, so i wouldnt have to bother with em.