Given that Russia is not facing an existential threat comparable to that of Nazi Germany, I don't think there's any way the conflict could be anywhere as driven as that.
Could Russia mobilize more? Yes, absolutely. But based on what we've been seeing they lack the supply lines, resources and frankly military competence (which is unsurprising given how Putin deals with anyone but yes-men) to be able to do anything with that if they had it. Also, as I said, the NATO response to invading, say, Poland would also look extremely different from the current NATO response to invading a non-NATO border state.
The Soviet Union's main advantage during WW2, other than receiving immense support from the Allies (both in supplies and military equipment), was that it was fighting the Nazis on their back foot. The Nazis had made a similar fumble as Russia did in Ukraine by misjudging the climate and seasonal weather and they also didn't have a reliable supply line. The Soviet Union did deal a devastating blow in Stalingrad but the Nazis there were pretty much stranded in hostile territory without support at that point and many soldiers were suffering from frost-related health issues. When the Soviet Union actually invaded Germany the Nazis' troops were already spread out all over Europe and into Africa and losing ground in the various occupied territories.
The Soviet Union suffered massive casualties and contributed more sacrifices to defeating fascism than any other country involved, but militarily its capabilities do not translate into any scenario involving modern Russia NATO analysts would lose sleep over. Russia is "holding back", yes, but so is NATO and especially the US. Even the "modern" equipment the US has started sending to Ukraine is decades behind on what the US military has available. Ukraine's stronger allies have very much been holding out on "the good stuff" and instead mostly cleaned out their dusty reserves. Russia OTOH doesn't seem to have the production capacity nor resources to churn out its newer equipment (which is still years behind what the US etc have access to) and is already falling back on decades old stock and desperately buying ammunition from North Korea of all places.
Could Russia mobilize more? Yes, absolutely. But based on what we've been seeing they lack the supply lines, resources and frankly military competence (which is unsurprising given how Putin deals with anyone but yes-men) to be able to do anything with that if they had it. Also, as I said, the NATO response to invading, say, Poland would also look extremely different from the current NATO response to invading a non-NATO border state.
The Soviet Union's main advantage during WW2, other than receiving immense support from the Allies (both in supplies and military equipment), was that it was fighting the Nazis on their back foot. The Nazis had made a similar fumble as Russia did in Ukraine by misjudging the climate and seasonal weather and they also didn't have a reliable supply line. The Soviet Union did deal a devastating blow in Stalingrad but the Nazis there were pretty much stranded in hostile territory without support at that point and many soldiers were suffering from frost-related health issues. When the Soviet Union actually invaded Germany the Nazis' troops were already spread out all over Europe and into Africa and losing ground in the various occupied territories.
The Soviet Union suffered massive casualties and contributed more sacrifices to defeating fascism than any other country involved, but militarily its capabilities do not translate into any scenario involving modern Russia NATO analysts would lose sleep over. Russia is "holding back", yes, but so is NATO and especially the US. Even the "modern" equipment the US has started sending to Ukraine is decades behind on what the US military has available. Ukraine's stronger allies have very much been holding out on "the good stuff" and instead mostly cleaned out their dusty reserves. Russia OTOH doesn't seem to have the production capacity nor resources to churn out its newer equipment (which is still years behind what the US etc have access to) and is already falling back on decades old stock and desperately buying ammunition from North Korea of all places.