Vehicles - the gauss hog aside - are very well balanced in Halo 3. In Halo 2, you were a rocket magnet, full stop.
You can go on long sprees in Warthogs if you 1) have a good gunner and 2) are playing against idiots who don't know how to take down a vehicle (i.e. randoms in matchmaking). Every map is littered with tools to take down Warthogs, which
one person can employ carefully to do so (I'm
very often that person). Aside from the laser and aforementioned gauss hog, the infantry/vehicle balance in Halo 3 was damn near pefection.
You show me a video of an epic (non-gauss) 'Hog spree, and I'll show you the 20 opportunities the other team had to toast it but didn't.