For both sides, the most important job for the nukes was counter-force, that is, blowing up the enemy nukes. Both sides understood this, so they deployed their own nukes so sparsely that you generally need one to take out one, and since they still expected to lose a lot of them, they built spares.
to me, it was the invention of SLBMs that truly but the concept of a first-strike advantage to bed. With subs under the water in the world's oceans armed with dozes of missiles each armed with multiple warheads the concept of taking out your enemy before they can retaliate is gone.
IMO, if MAD fails it will be an accident that triggers a run away chain of events leading to nuclear war. We've come close many many times to total nuclear war due to miscommunication, simulation errors, procedural errors, etc.
