Bro wars last for years and during wartime technologies sky rockets. If you know your Russian history you know they never surrender they always retreat and live to fight another day and they are masters at stalling war and battles. They would have weathered out the storm for years, regroup and then fucken throw every nuke at us. By 1948 they where nuked up big time. You can not defeat an enemy in 1 year, especially Russians, the bigger the land the longer the war and Russia has the biggest land mass in the world.
I certainly agree about the Russian mentality and ethos toward warfare; they'd consider just one Russian standing at the end a "win" if it meant all of their enemies were dead.
However, it's not quite accurate that they had an appreciable nuclear arsenal in the late 40s. Everything I've studied suggests that they were at a distinct strategic and tactical deficiency when it came to fighting a nuclear war with the U.S.
I'm not saying the Soviets wouldn't do horrific damage. They would have, especially as the decades went on. But as I said, the most reliable sources I've read all agree: the Soviets didn't hold back on the button because they were afraid of M.A.D. They were afraid they'd lose, and fairly badly.
I can dig some of those sources up if you're curious to see them -- just give me a little time. My granddad's mental training wheels fell off and most of my time's spent trying to figure out how to keep him out of a nursing home. (Note: playing grab-ass with the home assisted caregiver is a BIG no-no.)