lol. Let's stop thinking about what's realistic, and start thinking about what keeps the game more fun. You think you'd call your heli and it would get there in 20 seconds? You think you could call an Air Strike and have it be there in 5 seconds? You think you could run through an air strike and not get killed? UAV? I mean come on. UAV gives you a map with little red dots representing every person in your area? How is that realistic? I don't show up on radar in real life, and there is no way that some reconaissance plane would be able to pick up everyone, even when they are in a building and out of sight. Respawn is not realistic. Last stand is not realistic at all. If I pump 5 AK 47 rounds into you before you go down, there's no way your just gonna whip out your deagle and then pop me and then the next 3 guys that walk into the room. Dead silence is not realistic. Bomb squad is not realistic. Sleight of hand? Perks and most of the MP dynamics are not meant to be realistic. If the game was super realistic it wouldn't be fun.
I will agree that the helis are kinda ridiculous, but I have seen game where it still doesn't get shot down even with the ridiculously low health. Maybe a little bit more health would make sense. Also, realistically, I should be able to shoot the pilot.
What I mean to say is that, while there are many completely valid arguments as to why the heli's health should be increased, the fact that its current low health is unrealistic is not one of them.