It's not how long they _last_, it's how many lives they take. USSR alone lost some 25 million people in WW2, mostly young, able bodied men. Some estimates put the casualty count even higher. Imagine the impact of taking basically all military aged men in the United States and sending them into a massive, five year long meat grinder. That's what this war was like for the USSR and other countries that couldn't wait until 1944 to directly intervene.

So yeah, I think it's great that we can no longer have major wars, and I think it's worth having the nukes if that's what it takes to deter others.