Halo 3 worked the same way, however in Halo 2 the amount of damage the player took was far more directly tied to the state of the vehicle. Once a vehicle receives visual damage, the player inside the vehicle takes significantly more damage from all non-direct sources (I.E, the vehicle getting hit instead of the player) making them really easy to deal with.
H3 had the same thing, but overall damage the player took from indirect sources was much, much lower. So they were a LOT less squishy than in H2.
In CE, vehicles were a total joke though. Yes you could splatter players on foot, but they were extremely easy to dodge, a single player with a Magnum could out-play and take out any vehicle with less than 3 magazines even if they never directly hit the player.