[b0rsuk]

Upgrades are designed in such way that Goliath benefits from them more than other aircraft.

Defense: +5% per upgrade. Goliath gains the most, while a Mohawk (helicopter) with 2 Defense upgrades blows up from a single Predator (default) missile. But you still need those 3 or 4 defense upgrades to survive a stray missile, or more importantly - a Prowler.

Speed: extra speed is not much needed on already fast aircraft, sight distance is limited and human reaction is limited.

Energy: it lets Goliath deflect and shoot more often. Others are not as energy intensive.