The RDA's most powerful asset is their spaceships, but in order for there to be a story the RDA have to not use them to full effectiveness. The RDA could just bundle up telephone poles and accelerate them in space towards the settlements of their enemies. No need to risk men in low altitude bombing runs that can be taken out by the Na'vi like in the first movie.
Otherwise, their other impressive asset is their city of Bridgehead, briefly seen in the second movie but mostly elaborated upon in the accompanying book on tech. There is a mile deep no-man's land perimeter around the city where anything that tries to cross dies, presumably killed by landmines and automated turrets. The RDA have an unassailable base. Presumably the only way the heroes will be able to reach it in the next movie will be to infiltrate it and deactivate the defenses from within.
The RDA can also clone bodies, clone people's personality and memories, and also remote control/puppeteer bodies from long distance. Theoretically, the RDA could acquire a DNA sample of the Na'vi leaders, secretly grow clones of them (either with new personalities loyal to the RDA, or just Na'vi bodies that can be remote controlled by the RDA), and then replace the Na'vi leadership in secret and make those tribes not an issue, either leading them away from the RDA's area or allying with the RDA. Could have also used Avatar infiltrators to stage false flag attacks and instigate conflict between the Na'vi tribes, distracting them from the RDA, or again perhaps incentivizing tribes to ally with the RDA to gain their support and weapons.
What even were guided missile launchers supposed to be used for?
Pandora monsters can be pretty big and heavily armored, so the missiles could be useful. Also for blowing up positions enemy Na'vi are taking cover behind such as dense rocks or thick trees.
