True, however they will at least recover all the pilots they lost historically in the Eastern Front not to mention all the aircraft.
Right, so 50% more at most if the East is entirely stripped of aircraft and pilots. More reasonably, 20% or so, with only a small proportion of that being additional modern interceptors. That won't delay Allied control of the air for more than a few months even being generous, not with the P-51 and later P-47 models pouring out of American factories.
There's not going to be any Lend Lease for the Soviets here, the Red Army can't be an endless juggernaut anymore. Also Stalin isn't going to jump in on the allied side just because he'll win eventually and suffer massive losses doing it when he can get the same gains right at the end.
Without Lend-Lease, the Soviet Army will be considerably less mobile or coordinated. On the other hand, it will be much larger without Barbarossa. And no, Stalin isn't going to jump on the Allied side. But he may well opportunistically attack Romania to place the Nazis even more over a barrel (ie making himself the only source of oil) and allow him to extort more, with said extortion likely making up a good bit for the lack of Lend-Lease. And this is all assuming that Germany does not strip its eastern forces to reinforce the west, and beef up air and naval production. If Germany does, then Stalin could win without the massive losses part, and he will attack eagerly.
3. (I hope tertiary) There is a disturbing undercurrent in 'western' thought of recrudescent racism. The whole - 'maybe they had a point' thing, which we sometimes see with reference to Israel. Some folks, in their squalid little minds, have convinced themselves that a Nazi victory would not have been so bad. Shan't even discuss actual nazi enthusiasts - luckily they get booted off the board promptly enough.
There's also the Pat Buchanan style people who may or may not fall into this classification. They do not think that the Nazis had a point (at least not openly), but they do have a truly appalling disinterest in any suffering by "other people." They dislike some the changes that occurred since 45, and blame it on the war, which they think could have been avoided had the West allowed Hitler and Stalin to do whatever they wanted with Europe. Most notable in this group would be British Imperialist types who think Britain should have rolled over to preserve the Empire, and American isolationists.