I agree with him frankly. Ghosts get pooped on by everything, and so do Choppers. Warthogs are the opposite. Besides, I don't see why scout vehicles even need weapon upgrades, just health, defense and speed upgrades.
Look at the upgrades available for the scouts.
Ghost:
Boosted Ram (Ability to ram)
Strafe (More effectively dodge grenades and rockets)
Scout Shield (Applies a small energy shield to the ghost)
Chopper:
Autocannons (gives ability to shoot)
Stabilizers (increase autocannon accuracy and damage)
Ramming Targe (increases damage done and decreases damage taken when ramming)
Warthog:
Gunner (applies a light machine gun)
Grenadier (a grenadier is seated in the passenger seat)
Gauss (the machine gun is converted to a gauss cannon)
Warthogs and Choppers are doing it wrong, Ghosts are doing it right. Choppers and Warthogs three upgrades revolve around attacking and causing damage. This is not what a scout unit should be doing, in fact a gun on a warthog only tells the opponent that they've been scouted thanks to the "Under attack" sound clip and the ping on the mini-map. Scout units are supposed to be about speed and efficiency, not combat. That's the last thing they should be doing.