Because people today want more realism in the ww2 flight sim and not 'fantasy'
Then perhaps you should abandon the notion that players should be forced to work their way up the aeroplane food chain. There is nothing at all realistic or historic about matching I-16s against Tempests. Your plan would still have them flying in the same arena at the same time.
The only way to make early- and mid-war airplane combat "realistic" is to place those planes in arenas which exclude planes from other historical time frames. We had this for several years, with Early War, Mid-War and Late-War arenas. Over time, players moved to the Late War arena, and the other two wasted away. This preference is not something that you can change, or that would be wise to change.
- oldman (who can't believe that he's fallen victim to the troll)