To win, you have to survive the final assault.

If it looks like you’re at Custer’s last stand, then keep firing... you’re almost done.

Watch for strafing crabs!

Protect the other MUTs whenever possible.  You need their firepower in the downtown area.

If you have a choice of targets, and one is a mobile cannon, then kill it first!

In the city area, zoom your top-down radar to 2km radius and kill the nearest objects first.

This is a long, drawn-out fight.  Conserve your ammo and use it wisely.