Honestly, any war that takes too long against the USSR only benefits the Soviets because it means they can keep improving their industry and builduing up infrastucture for both war and civilian use, combine that with the Soviets seeking only to defend themselves(for now) and any advance is gonna be much more difficult if not outright impossible as even the strategy of "indepedence movements" will be fought both against loyalists towards the regime as well as the Soviets counter attacking and because they're not pulling a Bagration, they're much better suited for small counter attacks to expell invaders and peraphs invade enemy territory.