Actually, about half of Russia is always around zero. Though, roughly the area from Western Russia to Moscow is pretty fertile in non winter months. Talk to xy if you want to learn more, I'm sure i generalized or was completely inaccurate and am now a fat American retard.
To conquer Russia does not need to take fast, because it is not really possible, nevertheless a huge country. If you can take it slow and orderly progress if the supply, unlike most war the army was left without supplies,
Barely any Hunnic territory was actually Russian. The land that was, was south Russian. Avars migrated, not conquered Hungarians migrated Turks migrated Timurids raided, not conquered Vikings didn't conquer Russia, it is even doubted that they sent people to found Kievan Rus Scythians didn't really actually conquer any kingdoms / countries worth mentioning. It was all tribes & stuff. Poland-Lithuania did indeed. Finland basically held their front, they didn't actually make much progress. (Still an impressive feat considering their size). Likewise, Kievan Rus' weren't actually conquering anyone to get the land. Just tribes. Goths migrated Uzbek didn't conquer, they just were in the same general region... By that logic, Kazan, Sibir, and a whole lot of other geographically Russian countries count as well, which they don't. Sweden did do it. Golden Horde did pick off a few weak Russian principalities, but that's about it.
By your logic, France also conquered Russia, but they just sacked Moscow and left. Not real conquest if you ask me. The Mongols kind of took over Russia. They amassed the territory, but they were used to the weather, and didn't take down many principalities from former Kievan Rus'. So let's look at a list of who actually conquered Russia (even - kind of)
Poland-Lithuania - Defeated in war Sweden - Defeated in war Mongols (to an extent) - Defeated a few principalities Golden Horde (to an extent) - Defeated a few principalities Timurids (This is REALLY stretching it) - raided Russian cities, including Moscow, no actual conquest. France (And this is really, REALLY stretching it) - sacked Moscow