If you zoom in and see their turret pointing at you, pull up!!! Then, grab a wee bit more alt and then try it.
I agree %100 that it is a travesty in AH that a tank can shoot down an aircraft with its main gun. The Hvy bomber-Stukas and gamin' the game dog-fighting Me163's as well.
A: tankers in WWII didnt concern themselves with the dive bombing or gun toting aircraft, their AA gun was a last resort and usually the enemy AT guns, tanks, and infantry were far bigger threats.
B: The IL-2 and Hurricane IID both came in a low angles (I forgot just how low). The 190F-8 fired its rockets usually under a 20 degree dive. It isnt that the aircraft in AH are doing anything wrong, it is just too easy for the main gun to shoot down aircraft. But, wudya do??? It isnt like HTC is going to spend time dry humping the code to limit any of the travesties I listed above. There are more important things for them to develop, so adapt and over come, or shush.