On any game, there is as much teamwork and caution as the player allows. That has nothing to do with the game mode. Battle is only life and death so the player's objective is to survive and kill. If a player goes into siege with the only thought to avoid death and score, he/she is not doing the objective.
I played on a battlefield 1942 server that had a 90 second spawn time and eventually I had to decide whether playing the game or waiting was more fun. I knew eventually, no matter how well I did, I was going to have to wait that minute and half to play again.
Battle is good, but ATS was the only siege server.