The game isn’t over if Bryansk is German controlled. In fact it’s true, against a German player which is not entirely incompetent and that has a minimum of dedication to play against the Russians, Bryansk is sooner or later German controlled. But here comes the difference of BM now.
While in vanilla Germans can simply go South from there, in case the Russians turtle, the economic advantage was very very hard to stop.
Now, in BM this is way tougher for the Germans, even if Germans are at 75-80 income, they now often have to match 15-20 additional IPCs by Russia/UK/US which makes it not as easy as before to turn the position into an economic edge.
Also the +3 for India makes a big difference. In vanilla Japan often could stack Burma after 6-8 turns without making an big concessions (such as e.g. use all transports for that). Now, in BM India has 4-6 extra units in average until this happens which makes it way harder to Japan to take India. (That-äs why I btw believe it is a bad idea to send the Russians home, it simply makes it too easy for Japan then to push towards Burma and keep the Chinese controlled.)
Still, if Japan is totally dedicated to get India, it often might not be stoppable. The game is not designed to make such things impossible, it just puts a higher price on the price tag.