Perhaps rather than a whole map domination or highest score victory there could be strategic points of interest on the map that should be the object of the game.
The winner / winning team is that that either is :
- first to hold all strategic points
- holds most at the end of a timed session
- has held for the longest period of time over a timed game
This next bit may make it too complex but it could be extended:
This could be continuous - after a timed period (say 1 day) theres a mini-victory, points and rewards given, the strategic points move randomly and starts a new mini-contest for the next mini-victory.
At the end of several time periods (say 1 week) theres an overall grand-victory for the winner of the most mini-victories.