Your entire argument is based on the Soviets being unable to change, adapt, or be anything other then a paper tiger. History shows that the Soviets can be very adaptable, and forward thinking in thier plans when they need to be. Just as Germany going to war with Russia in 1943 gives them more time to prepare andbuild up forces, it does the same for the Soviets. This of course also depends on if the UK is still involved in the war plan you map out. With them in place maybe the Soviets still fall for "we need all these divisions East to keep them safe from British bombers," but if the UK has already fallen or accepted peace Stalin will not buy it for very long.
We cannot on the one hand point to the Soviets as foolish, ignorant soldiers and at the same time look at history with an unbiased eye. History shows the Soviets were in fact good soldiers, planners, and can win wars.
You miss understand. In the same way that Hitler crippled German War effort, so to did Stalin until war actually began. He was repeatedly warned by many sources about the nazi threat, but choose instead to follow his own instincts on Hitler.
The longer the non-aggression pack lasts, the more his instincts would be validated. Yes The Red Army would rebuild and improve, but only as a peacetime army so in effect little progress at all. They would still have the same doctrine that would fail them just as well in 1943 as it had done in 1941. Many of the Soviet divisions that fought in 1941 had been in existence for decades and they only performed marginally better than the divisions raised months before the invasion.
Germany on the other hand was in an active war and learned allot from their initial clashes with the west. So they would be able to refine a very successful operational doctrine.
When war came yes the soviets did learned from their mistakes slowly and painfully. If the Germans give them years of warfare, they could eventual rebuild to drive the Germans out and repeat history, but that would take some kind of miracle.