Also, if you make completely a-historical decisions, such as saving the whole of 6th Army, you have now changed the balance of forces dramatically and you are in what-if land. Perhaps the Axis attack would have been unsuccessful if the Soviets had been better prepared? If the AI appreciates this and decides to hold, that's not necessarily a sign of a bad AI. Let's not forget that the real Case Blue led to Germany's greatest military defeat.
A really good Axis AI would make peace with Great Britain in 1940, sign a Pact with the USA, never invade the USSR and build farm implements instead of tanks from 1941 onwards!
By 1940 it is too late for Germany. A really good Axis AI would stop while Poland and Czechoslavakia still provided a buffer against the USSR.
After all in 1940, Germany did try to make peace with GB, but even if they had succeeded, by 1943 30,000 T34s would be ready to roll from inside Poland.
Well, yes, if you buy into the theory that Stalin was only biding his time before attacking Germany, with the forward posture of the Soviet army cited as supporting evidence.
The contrary view (which I find more compelling) is that Stalin was terrified of war with Germany and would have done almost anything to avoid it. The forward posture of his troops merely reflected conventional wisdom that attack was the best form of defence in the event of a war started by Germany.
Furthermore, an attack by the Soviet Union would have met a German army fighting on a single front and fully rested and equipped since it's highly unlikely that Hitler wouldn't have appreciated the threat. The Soviets meanwhile would have had no lend lease to depend on and no allied bombing campaign to diminish Axis production and logistics. There is a strong possibility that the Axis powers would have defeated the USSR in Eastern Germany/Poland. Also, let's not underestimate the effect of having been invaded in '41 on the morale and spirit of the Soviet soldier. How would he have fought during a war of aggression?
The other big what-if is whether Japan would have launched its attack in Asia if the western allies were not engaged in Europe. With peace in the Pacific, the potential for Japan to attack the USSR from the east, given a defeat of the latter in Poland, certainly needs to be taken into account.
Let's not forget also that Communism was considered an even greater menace than Fascism by many western leaders. How the west would have responded to a Soviet move into neutral Poland is anyone's guess. It's entirely within the bounds of possibility that the western allies would have assisted Nazi Germany in those circumstances, regarding Hitler as the eastern bulwark against the Soviet horde.
The bulwark idea would work before Germany and Russia split Poland, after that, the West ceased to find the Germans anything other than dangerously opportunistic especially when it came to dealing with Russia. Which is why 1940 is too late. The bulwark against Russia was supposed to be Poland and Czechoslavakia. Also by 1940, the German economy was already heading steadily down hill. See The Wages of Destruction: