While the team stealing ideas would have an objective the other team would only need to kill everyone on the other team to win. Now the team stealing ideas would have to go to the third level and someone would need to left behind at each level to protect their bodies and later give them a kick.
When a defense force member is killed he is sent to a random level away from combat and when a thief is killed he is sent to limbo to wait to be saved. The thieves will be more powerful, skilled and will know what the map looks like though so that means they should get killed less often.
Overall it should be a balanced experience that will hopefully feel original.