Quad spam can be potentially very powerful. Gameplay-wise, one should be able to avoid their powerful missiles by hiding behind a building or a wall.
It doesn't necessarily make much sense that a vehicle low to the ground should be able to shoot over things perfectly. Same for infantry.
The advantage of shooting high should be reserved for units like artillery, so you can put them behind walls or other obstacles. Makes gameplay more interesting and dynamic.
TowerRockets will stay high.