78 billion dollars of bottled water is a weapon.
That's a lump of ice the size of a small moon (Or only maybe Greenland if it's Fiji Water rather than generic water... Gods imagine the damage 78 billion dollars of tap water could reak?) ramming into the side of their planet.
They designed a fleet to take on another fleet, but the kid said fuck it, lets take on the planet.
If they had talked to the Engineers to design Planet Busters instead of articulate drone fighters, the final engagement would have been completely different and succinct.
Until Churchill got really drunk one night half way through the first act of WWII and said "Fuck it, lets just kill them all" which sanctioned Germany's civilian population as viable targets, the Luftwaffe was almost civilized in their disciplined surgical attacks on military assets up to that point.