Not much to this idea. If you remember the Fighter swarm rockets then you may understand the concept well enough.
Give the Dropship those little swarm rockets. Effect should be similar to Railgun Tank missiles. Pepper an area with explosions, enough to ensure that no light units can survive.
Also, give the machine gun more ammo and more damage. Let the pilot focus fire a big target like a tank or scorp if necessary and punish it hard.
Do this and the Dropship will become more combat viable. Its still a sitting duck for any tank in the area but it has some teeth and can serve as infantry support either through focus firing a tougher target or clearing an area of infantry/lesser aliens.