"in game it will shoot at you from more than double that how come?"
2000 meters is just over one nautical mile. In the game, I have not experienced an aircraft firing at ranges over 2 nautical miles. Nor would I expect an aircraft to be able to hit a submarine at over 2 nautical miles with a fifty.
As for the damage. Having had the pleasure of firing the fifty, there was little that could withstand a concentrated fire of a .50 cal. Given enough rounds, it will chew through pretty much everything.
There are just some weapon systems that don't need no improvement
