Create a reward system for all classes in addition to accumulating XP. For example, Medic would get a visible reward like a weapon or uniform skin after reviving 100 players. Or, Recon after that lacing 100 spawn beacons. Engineers after fixing 100 vehicles. Have different tier equipment to unlock like a better version of the defibrillator, drill, spawn beacon. This will encourage and reward players and show their commitment to others.