After a brief analysis (I played the game), I have found the following:
My initial premise was not entirely correct. However, I did find problems with the Gargantuan's AI. The Gargantuan displays a "lazy" behavior:
1. When sent to attack a building or non-moving target from a location not currently in range, the Gargantuan will only advance enough untill the point where only 1 turbolaser can fire, or is in range (this will only change if the target approaches the gargantuan, and as more weapons come into range they will fire).
2. If the Gargantuan is firing on a target, and then is told to switch to a target that is already within range of at least 1 weapon, it will not move to fire more efficiently (only weapons in range will fire, vehicle will not move to use more).
3. The Gargantuan does not change position when firing on targets of different classes (i.e., infantry, vehicles, buildings). This means that no matter the target, the Gargantuan's behavior will follow 1 and 2.
My conclusion is that if a change will be made, it should somehow focus on making the Gargantuan more aggressive and efficient.
(this analysis is drawn from brief gameplay. If anyone finds something different, please post it)