Germany went and ticked Russia off. If the Non-agression treaty had held, I'm sure Stalin would have turned his attention to China as soon as Finnland was down for the count.
And Russia had literally just a few months to decide how it wanted to carve up occupied Germany and the rest of Eastern Europe. Settle on which troops to take out of the occupation force to send against Japan, actually MOVE them, transport them to the Russian Far East, draw up a plan, and then build up the needed logistical support before the USA hit them with the A-bomb.
You seem to have NO idea, not even a clue, how hard it is to move armies around when its more than just marks on a map.