It's not a sheer numbers game but also the fact that the Russian army is so useless and ineffective, that superior numbers can't make up for the hopelessness and demoralization of being an incompetent soldier sent to die in a foreign land for the ambitions of one corrupt and incompetent ruler, in a war that you don't really want to participate in. When one Ukrainian fighter equals ten or more Russian soldiers the odds aren't exactly in Russia's favor. Many have already deserted the battlefield and many more will.