First of all normal (air filled) baloons are falling too quickly (the aerodynamic drag they make is too small or the mass is too big).

2 setmass command is not working for them.

3 Water baloon dropped from just 4 meters can kill a guy wearing a helmet. If this could be real workers on building sites would not wear helmets because brick dropped from 5cm would break their helmet, head and even torso ;-) To be honest water baloon in game is more dangerous than brick in real life :D
Water baloons should kill, but not as easily.

4 When you drive over baloons with quadbike they will NOT break but your quadbike can easily flip (WTF?! Baloons stronger than quadbike??!!). When you drive over them with heavier tracked vehicle they will sometimes break, but not too often and your vehicle will have problems with driving trough them. You will rather not flip but it will not be a soft ride, even if you drive IFV. Thats crazy, baloon strong.

5 When you shoot trough baloons with water bullet easily penetrates so many of them. IRL water is quite effective bullet stopper and it should be aswell in game.

6 When you drop air filled baloon from something like 7-8 meters it will always pop. In real life they do not pop as often when you drop them from 8 meters.

Last thing: I requesting hellium filled baloons. Also nitrogen filled ones would be nice.