That’s pretty wise–especially since if Japan remains at peace with Russia for the whole game, they give Russia 20-40 extra income from the East. If you trim off the Soviet East from every direction, they are in much worse shape.
However, recall that there are 3 nonadjacent territories that Japan can attack with impunity; so the decision more hinges on when than if. All going to be dependent on whether the Russian player hides those 18 men effectively or lets them die for no reason.
Japan wants all that stuff dead so that it doesn’t have to garrison its heartland, either. The problem there is that many strategies eschew the northern factory placement and argue for either all transports, or a base in Malaya or FiC (or hong kong–this one is very versatile). Those bases give you more mobility and pressure on India.
And as part of my “5 Spicy Allies” battle plan, Russia is crucial; it has to pull that attention northwards the whole game. Every unit/$ that goes up there means a slower Japanese moneygame and endgame development.