This is a thought experiment so, please don't try and discuss in detail how production or pilot numbers or, something like that couldn't happen. In this What-if its PFM... Leave it at that.... What if the Allies (including the Soviets) were never able to achieve air superiority over the Luftwaffe? What if the best they could manage was parity. That is, neither side had superiority and both were operating both defensively and offensively throughout the war? We can see some of what might have happened from the WW 1 experiance where this was very much the case up until very late in the war. Of course, aircraft then were much less sophisticated so the impact on the ground war was less. I would say that it wouldn't have made that much difference in the overall scheme of things. The Allies would still win albeit with somewhat heavier but not unbareable casualties. I actually think that tactically, air superiority wasn't that much of an advantage that it couldn't have been compensated for. This is one reason the Germans remained relatively effective in ground combat almost until the very end of the war.