I believe little bird vs armed 4x4 (technicals) are the classic showdown. however, it seems the 4x4's gunners are way to accurate. They can kill the pilot of an little bird who is flying at a speed of 50 while the 4x4 is also moving at a similar speed.
to reproduce. simply create mission with 4x4 and a little going at each other. put your self as a little bird pilot and try to take on the the 4x4. you will notice the 4x4 taking you down from about a km or 2 away. now switch position and play as the gunner of the 4x4. you will notice it's is very difficult to shoot down an fast moving little bird from a moving vehicle. Similarly you will notice the helicopter being very accurate where as when you were flying you would have notice how difficult it was to a) spot that little 4x4 and next to actually aim at it.
I believe currently vehicles (little birds and the 4x4) are able to shoot accurately from a greater distance while both are moving. This is not accurate. there accuracy should be affacted by their own speed as well as the speed of the target (similar to infantry combat). Secondly there ability to identify target should be toned down. It's not easy to spot a 4x4 from a little bird. similarly it is not that easy to spot a little bird from a 4x4 unless they are up close (less then a km).
I also tried the adjusting the gunners aim difficulty setting to 20 but that had minimal affect.
Thanks