It might work 40% of the time but it's not anywhere near the best option. The game is almost always won/lost inside the city. If your team lemmings down the valley you can try to defend, and there's more potential for that to work.
What are you going to do when you've pushed through, they're at your base and they're controlling everywhere else on map, resetting whoever's left capping on their base while you and your teammates futilely try to fight off their cappers AND defenders with your already disadvantaged team?
Just let a couple people do whatever they want in the valley, while yo