What if the Russian player lends a fighter to the UK fleet on Rus1?
That makes the odds a lot stronger for UK.
Sure, makes the odds stronger for UK , but means that russian ftr is gone from the Russo-German front for AT LEAST two turns (R1+R2), possibly forever, without providing a single offensive diceroll (it cannot participate in any battle during R1, and also reach BEN).
It results in making trading more costly for the Ruskies, during R1+R2. Russia needs to expose 1 arm/turn , to get the same offensive power to trade land with the Germs. That is a cost of 5 ipc/turn, since that ARM will surely be killed. Furthermore, it might make it possible for Russia to only attack 1 area (WRU) during R1, instead of normal 2 (+BEL or +UKR).
The return is that Japan might loose extra naval units/ftrs, but the combined cost of exposing ARMs, plus the weakened attack power on R1, just doesn’t seem to be worth it. After all, even a combined SZ30 UK fleet, is something of a sideshow. The Russian-German border is the main theater of war.