By when? The Japanese industrial base wasn't sufficient to do this on short order and likely wasn't able to do this at all without diverting resources from other areas. As such I don't consider this assumption to be credible.
The end of 1937 would be a good stopping point, after the Battle of Shanghai and capture of Nanking and northern Shanxi (please, no mention of stuff that breaks forum rules, I don't want this thread to close too). From that point the Chinese would likely sign a peace treaty. That gives the Japanese 4 years to build as much equipment as possible.
by june 1943, SU had 43 divisions there.
Quick tangent, can you provide a source as to whether those were actual divisions or paper divisions? The Soviets had a habit of conjuring divisions from thin air, but some had no more than a brigade's worth of troops and equipment. That's why in most discussions of the Battle of Moscow people talk about the manpower equivalent of how many divisions were raised, since more divisions were raised than actually filled with soldiers and equipment.
As has been explained a few times, the forces in the East were not a decisive factor in stopping the Germans in 1941, they wouldn't have had an easier time until well into the winter, by which point the logistics elements which you consider 'irrelevant' are taking a major toll on the German ability to maintain offensive operations.
Again, arguing a point that hasn't been made. Show me where I said that those divisions were necessary to save Moscow? My point, and I'll bold this so you actually respond to it this time, is this:
The increased strain of fighting a two-front war, with a Japanese invasion of Siberia (in 1941 IJA forces totaled 1.7 million men, and by 1945 they had 5.5 million. They would have undoubtedly mobilized more men if they were planning to go toe to toe with the Soviets) would put a massive strain on Soviet forces starting in June. By the time winter comes around, the Soviets will have had to reinforce and resupply 34 divisions engaged in active combat for six months. That's also assuming they don't send more divisions to the east, which they undoubtedly would. This means that the Soviets would either ignore the Japanese and focus on the Germans (which would still put them in a much, much worse position with the Germans), or reinforce both fronts and give the Germans a much easier time. There would also be a qualitative difference in Soviet forces, as the tactics Zhukov developed would not be discovered at that time. Zhukov would likely be sent east (as until December 1941 Stalin had more faith in Timoshenko, so he would most likely remain in command).
Unconditional surrender and huge swaths of the Soviet Union being annexed.
Not unconditional, and annexation to the Astrakhan-Arkhangelsk line. I doubt they would have completely held to that, since they had Brest-Litovsk as precedent. If the Soviets lose Moscow, Leningrad, and Stalingrad then it would be relatively easy for the Axis to threaten Arkhangelsk and Astrakhan, so it's not entirely out of the question, but again I doubt Hitler sees it as worth it. However, given that the US won't be joining the war anytime soon and the UK can't really threaten the continent on its own, they have time and resources to work with. This is to say nothing of the Japanese who would have cut off Siberia. Also remember, if the Germans take the Caucasus there goes the Tehran lend-lease route, that supplied huge amounts of military equipment (enough to supply 60 divisions by US standards, more by Soviet standards).
Assumption #2 has a huge amount to do with this, however you'd like to ignore the logistics challenge in defeating the Soviet Union it's there none the less.
Not ignoring, and it has nothing to do with it. You're talking about two entirely different timelines. The Soviet force composition in 1942 in this timeline will be radically different than their force composition OTL. You might see a push for Leningrad, or another push for Moscow. Either war, the resolution of one of those fronts would greatly reduce the logistical strain, and at the same time the Germans will have more time and resources to devote to improving logistics.
You seem to be failing to grasp that the Soviets had other things to worry about then their favorite pastime of cutthroat politics during the war.
On the contrary, there's no better time. If there was the feeling that the Soviets had completely collapsed (evacuation from Moscow) it would be very easy for Beria, for example, to kill Stalin and take his place.
Wartime is commonly where the cutthroat politics happen throughout history, from Rome to Russia. Just ask Leon Trotsky about murdering political opponents while they're fighting alongside you as allies.
Once again we're talking about what the Germans can accomplish so the according to you 'irrelevant' German logistics challenges have their effect. Time isn't in favor of Germany in the long run, even with the Soviets under more pressure Germany will be losing North Africa soon and start losing Italy. The Luftwaffe will be stuck in it's death-spiral of over-commitments and lack the personnel and equipment to regain or build strength.
How do they lose Italy? The US isn't in this war, Pearl Harbor didn't happen. Without a direct attack on the United States or invasion of the Americas (remember the Monroe Doctrine), they probably aren't joining the war. It took until 1943 for the Axis to lose Italy OTL and much of that was due to Operation Torch (carried out by the US). Without that, there's just a continuation of leapfrog warfare back and forth across the desert.
The German land forces will fare better of course in facing less counter-attacks from the Soviets but will still have few good answers for how to capture a city like Moscow, Leningrad or Stalingrad. Without accomplishing this as time passes after Barborssa the overall pressure on the Soviets is reduced, even with Japan's efforts as the Soviets get a handle of things over the winter and stabilize the situation.
Here is where you miss how critical lend-lease was. Without the Vladivostok route, the Soviets have to produce more food, trucks, locomotives, radios, machine tools, etc. That means fewer tanks, planes, rifles, artillery pieces, etc. That means fewer draft-eligible men. That means less equipment for frontline troops. The Soviets would be forced to try and dislodge entrenched Japanese in Siberia (no easy feat as they would be hundreds of kilometers from Irkutsk), while simultaneously launching futile counteroffensives against the Germans. The pressure is on the Soviets here, as it was OTL.
As for Moscow, Leningrad, and Stalingrad, there are answers for those. Operation Nordlicht was to be the final assault on Leningrad in 1942. If this had been coordinated with the Finns and didn't happen to take place at the same time as the Sinyavino Counteroffensive (which likely wouldn't have been nearly as potent if the Soviets had to supply offensives in the east), then it is likely the city would have fallen, or at the very least been heavily contested. All routes of supply would have been cut, which means it would be only a matter of time before the city fell.
In Stalingrad, the Germans have much more time. If Leningrad is captured, that frees up many troops that can be redeployed south. The Soviets would not be able to sustain enough forces to defend Arkhangelsk and attack the Japanese in the east, as well as build up forces against Army Group Center to distract the Germans from the forces gathering for Operation Uranus. Essentially you have a German High Command who sees that the Soviets are building up in the south, and redeploys troops from AGC and AGN accordingly. Uranus doesn't happen (also because AGS mobile reserves aren't withdrawn to Italy), Stalingrad falls (as it was close to doing anyways, by the end of 1942 the Germans had reached the Volga, occupied 90% of the city, and the Soviets were left in two small pockets). With the forces from Stalingrad freed up and the Soviet counteroffensive defeated (if it was even attempted), the Axis is free to send more forces south to the Caucasus.
Finally, for Moscow the end would be in sight at this point. The Germans are now experienced in Stalingrad-style warfare, and they don't have the drain of Leningrad and Stalingrad to worry about. The Soviets would be scrambling to put enough troops on the line in both the west and the east. The Germans could encircle Moscow and engage in street fighting until the city was taken. Without petroleum from the Caucasus (even if the Germans don't take it entirely the supply line is cut) and from Vladivostok, the Soviet ability to counterattack and conduct defense-in-depth would be severely limited.
Yup, and they'd be right about that, minus the Yamatos and Shokakus you could easily see the British more active and aggressive in the Pacific along with the Americans accelerating the Japanese collapse there. This whole thing would basically be a sacrifice play for Germany's sake that only makes sense in a game-world, IRL the Japanese didn't want to sacrifice their empire for the sake of the German one.
And why would the Americans be involved? In addition, IJA gets preference if they're taking on the USSR. Remember that the main cost to the Japanese would be moving 50km from the Manchurian border (and even then only in some places). From there they have to set up defenses in
very favorable terrain, build fortifications and supply depots, all the while maintaining safe distance from Irkutsk to ensure the Soviets can't supply sufficient forces to dislodge them. Meanwhile, the Soviets would be launching futile counteroffensives.
