Versus just the European NATO nations, Russia would stand a snowflake’s chance within a blast furnace.

Just looking at Russia’s military performance in Ukraine gives you the answer.

• In 3 years of war, and over 800,000 casualties, Russia controls a piddling 20% of Ukraine. European nations (total) have far more territory.
• European NATO nations wouldn’t have restrictions about hitting targets deep within Russia. Bye bye, oil depots…on day one.
• European NATO nations wouldn’t still be buying Russian oil a year into the conflict. That would stop…on day one.
• Against European NATO, Russia’s aviation wouldn’t go up against 80s Soviet tech (and fail to achieve air superiority). Russia would be facing Typhoons, Gripens, Rafales, and F-35s, armed with long-range Meteor missiles.

• European nations have more advanced hardware…they already have it…they don’t have to wait for somebody else to dither around for months, or years, before finally sending it.
• European nations have already trained on their more advanced hardware. There’s no waiting for months until crews have been trained to read controls in a foreign language, and understand a decades newer system.
• European NATO nations actually have navies. Russia couldn’t defeat a country without a navy!

Russia entered combat with Ukraine with nearly every conceivable military advantage (except training, competent military leadership, and logistics expertise), and has managed to repeatedly fumble the ball in the ongoing war.

If they couldn’t beat Ukraine, they certainly couldn’t defeat Poland…alone, or Finland…alone, and certainly not all the European NATO nations!

The short answer is yes. Russia could overrun Poland and its three small neighbors: Estonia, Latvia and Lithuania. But it would be no match for the combined might of Germany, France and England all three of which have militaries with first world technologies. Germany, France and England are no longer considered great powers like they were in the Victorian era but they are medium sized powers and together carry a lot of heft. Let’s remember that Russia’s economy is approximately the size of California’s. If Russia exhausted itself fighting the backward Ukraine, how poorly would it fare against three medium sized European powers with first world conventional armies? Yes, Russia might overrun Poland but the moment it reaches the German border, the Russian army would be either repulsed or smashed and that’s just on the ground. German, French and English high tech air power would defeat the Russian air force in short order. And this is with no help from the USA. Russia is not the world power that it used to be.