Eh what? Russia was losing disastrously that was what caused the Revolution in the first. You don't seem to have heard of the Keresnky offensive. Germany already conquered the richest regions of RussiaI bet you if the October revolution failed people would say shit like "why would Russia fall to revolution they were winning. Ignoring the fact that wasn't their first revolution.
Stab in back myth only believed because Germany won the Eastern front whereas Entente never even reached the German border. In the eyes of the public Germany never lost the warYou do know where the phrase Stab in the back comes from right? Yes, I'm aware of the tale from King Arthur.