Parachutes are off? Then why the hell are you letting him beat you guys to the end? Problem solving. Use it! He beats you to the end because you fail at the map. Thats not his problem. His goal is to stop you. I would say he did a pretty good job.
Its not prenuking when it takes two min before the final doors open and you have more than enough time to go through all the obstacles. I have seen instances where zombies have beaten the humans up there and they were able to kill the zombie and win the round. Why can't you?