I believe you Kedde. I guess I am talking more based on my personal experience.
Depending on how scoring works and the benefits of holding resources, it may actually be more beneficial for the 2nd strongest team to slaughter the weakest team rather than working with them. You see that in RTS all the time.
On the other hand, since you can't actually kill anyone permanently, 1000vs500 will probably always be the better choice for taking down a strong server.