Are you serious ?
So you are telling that nothing destroys hydra but a rustler ? Well I sometimes go cop and destroy the opponent's hydra, it's not hard. It's pretty balanced, terrorists rush to the LV airport and cops rush to the old cop spawn to get hydras.
Hunters are too powerful and tanks are pretty useless, so I give - for adding any of them. The team who gets the hunter will have more chances to win and a hydra can easily destroy a tank whereas a tank can't do anything towards the hydra.
In case of president's survival, I saw some presidents surviving by roaming in the map, or using BMX, it's just if a police has a hydra, he can easily destroy the terrorists hydra because terrorists aim at the president and the cops aim at terrorists.
So, simply being security is not enough in NSA map.
I would simply suggest to add one more hydra in police hydra-spawn area.