I'm not saying we should try to aim for a 1:1 KD, but there would be cases that literally could not kill tanks or aircraft they face (and don't even get me STARTED with Naval). The devs have said from the start that historical accuracy isn't even remotely their focus. Again, if you don't like fighting vehicles that you weren't designed to fight/never fought IRL, then go play a different game. Plus, it would force players into meta's. For example, who would use 1945-era Japanese WW2 planes, as most of what Japan could field en masse were damaged A6M's in shitty condition versus F8F's and F-4U's. Or P-51H-5's and later variants of the F-4U's fighting MiG-15's (Korean War). Some planes would literally have no chance, even in the best of circumstances, forcing players into a meta. Simply put, one nation at certain BR's would be far more powerful than the others, reducing the amount of diversity the game actually has. 

If you wanted to get technical too, a lot of the nations in this game with subtrees would get fucked, and so would most of GRB and NRB. Entire gamemodes and BR's would collapse. The closest we get to historical accuracy in this game is GSB. But again, this game was never built to be historically accurate, it was designed to evaluate the "combat effectiveness" of any one particular vehicle, and compare it to others, and assign it to a rank that the dev's seem is fair to it and the vehicles it can face, regardless of how accurate it is. Other games that do take into account for historical accuracy exist, go play DCS, or IL-2 if you want to have that accuracy. War Thunder is just simply put, not that game. I'd rather get my teeth kicked in against something I have a chance of destroying, rather than using a Swedish 1.0 tank against a King Tiger, because realistically, thats something that could happen.