> You can study histories and interviews from the late Cold War about just how much of a bloodbath the NATO militaries expected a Russian invasion of West Germany to be.
*With the full benefit of hindsight*, most experts that I have read seem to agree that (ignoring nuclear weapons and staying completely conventional) the Russians were as a whole stronger on land in Europe than the west up until the mid-1970s, when western technological advancements started to remove the numbers advantages and were hard for the economically stagnating communist countries to keep up with. By the mid 1980s, the only real direct advantage the soviets had was a closer supply line than the bulk of NATO's power, which was the USA.
There are records showing the shock that Soviet military experts had at the effectiveness of the western stealth and jamming equipment that was used in the 1991 Gulf War (that was waged right at the tail end of the USSR's existence). It's much more regarded now that had a full blown NATO/Warsaw pact conflict occurred in the 1980s, the Soviets would have likely lost had they not effectively destroyed NATO's air power early on, though to be fair most experts in the west weren't as sure just how effective their kit would end up being.
Even taking air power out of the equation, the armoured kill ratios would have favoured NATO if it was even 1/4 the ratio it was against the Iraqis. Again here, the only advantage the Soviets would have had was if they got complete surprise before NATO could mobilise.
> NATO would have been fighting them AND the entire Warsaw Pact (East Germany, Czechoslovakia, Poland et al).
There are mixed signals in the archives we have access to about how well (or more accurately reliable) a good chunk of the Warsaw Pact would have been if the cold war turned hot. Half the Red Army's presence in these countries was to threaten them and keep a lid on any revolutions that cropped up (as they did inCzechoslovakia and Hungary as hard violent examples, and Poland in the early 1980s as a soft one). It was very nebulous with Romania in particular that it would participate in anything other than an full "unprovoked attack" from NATO.
> The Soviets wouldn't have had 30+ years of Russian societal decay and would have had the advantage of sheer mass.
There was already decay by the 1980s. Corruption was rife in the Soviet army, especially during and after the Afghanistan conflict. There are many documented cases of Soviet officers in Europe selling fuel earmarked for the army to local civilians, among other things. Many also participated with opium smuggling from Afghanistan to Europe as Soviet officers had some freedom to move around western parts of Germany unmolested, in particular West Berlin.