@Back, it was big team battle...Vortex I think it's called.
This thread took a little different direction but that's cool. If we are going to talk vehicle design philosophy, it seems that they want vehicles to not be power weapons as much as they want them to serve support roles. In previous games, we could use the vehicles in offensive aggressive playstyles. That isn't really an option anymore. The Covenant vehicles seems to be the weakest of the bunch (in strength.)
To use this support weapons more effectively you have to pay attention to map orientation and where the enemy is. I have found that the enemy is attracted to vehicles. Tantalized by the idea of getting a double kill. Well you can use that to your teams advantage. If you have teammates that keep your vehicle in eye sight, anyone that tries to come destroy is is easy pickings. If the enemy ignores you and tries to take out your ground troops your gunner lays down suppression fire, either killing the enemy or weakening them up for easy clean up kills for the ground troops.
That being said I would make a few changes to the vehicles if I had a choice.
Wrath---a little extra armor
Ghost---a lot of extra armor, but more driver venerability (should be able to hit the driver's head facing the ghost at the same level)
Warthog---increase armor so that it takes three plasma grenades to destroy OR faster acceleration and increased responsiveness
---gat hog (one of the following)
decrease gunner venerability (increase survival chances in mid range battles with DMR's)
increase fire rate of gat
increase range of gat
---missle hog
make the missiles function like the mantis, with either a single shot (more accurate) or overload barrage (with a spread)
---gauss hog
no other changes needed
Scorpion---increase mobility and armor slightly
Mongoose---increase top speed, reduce armor substantially
Banshee---increase armor slightly, not to Reach levels, but make it a formidable task to take down
Mantis---Make it a one shot Spartan laser kill, with how maneuverable it is a good driver won't be taken out by one at the current two shot