I think a good way to balance these types of things would be as follows.
For the targeting laser itself:
1) It is only carried by reinforced armor.
2) The targeting player can not fire any other weapons while using the targeting laser.
3) The beam of the laser is colored to match the empire and is highly visible. This way once you paint a target the enemy knows where you are. But since it's a reinforced armor they have a chance to last a reasonable amount of time (as in a sniper doesn't own them in 1 shot 2 seconds after painting the target).
The bomber:
1) Basically a galaxy except without the guns and with lower hitpoints. This would make it require an escort to hit the target which means more coordination between team members is needed.
2) Two types of bombs chosable by the bombbadeir. EMP which would knock out vehicles and maxes in the area for some amount of time. Another anti-infantry bomb that on impact scatters into several small fragmentation gernades. Dealing large damage (not nessacerily leathal to reinforced armor, but it would hurt them bad enough to make them easy for allies to kill) to lighter infantry but minimal damage to MAXes and vehicles.
3) Only fires if a lock on the painted target is maintained by the bombadier.
4) Only one bomb run per flight. So the bomber has to be rearmed before making another strike.
The artilery:
1) A slow moving tracked vehicle that requires a 2 man crew (pilot, gunner).
2) The gunner can only fire the gun when he has a lock on a painted target. This does not require direct LOS, so you can fire over small hills.
3) The vehicle must deploy bracing legs before it can fire and must retract them before it can move (like those giant construction cranes do). This makes it almost defenseless if unescorted.
4) The shells the gun fires have a tracer on them so the enemy knows where they are coming from even if the gun is over a hill.
6) The gunner can select from anti-infantry, or EMP as with the bomber, but each shell is considerably less powerful than each bomb.
7) The reload (or cooldown) time between shots is considerably long so that more than one of these vehicles is required to maintain an effective barage.
Misc:
Both targeting weapons require a couple seconds to lock on. This way, a skilled targeter may be able to move around while still keeping the laser pointed in one place long enough for a lock to be aquired, but it would be very difficult to do in the heat of battle.
I think that would make the weapons pretty well balanced. They could always be negated by killing the reinforced that's carrying the targeting laser and the vehicles delivering the weapons are very vulnerable without a signifigant escort that could otherwise be directly involved in the battle.
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