The issue is that (again with hindsight), the “expand into the ussr” faction of japanese leadership had already been solidly defeated by 1939 by the “expand in China” and “expand in SEA” factions, so there was no possibility of the border skirmishes expanding to a full second front. And Japan already running into overextension problems and the limits of their production by 41. So again, while I get why the soviets made the choices they did at the time, with hindsight it seems like the wrong choice imo