Surely the threat of mass destruction had more to do with that so-called peace.

And was it really peaceful? All that espionage essentially led to the proxy wars across the globe that cost countless number of lives.

How many people died in WW2 vs all wars after WW2?

Why?

Proxy wars and spying kills less people than world wars. It's objectively better.

It's only objectively better until another world war comes - we are not immune, and then, it will be easily objectively worse. This argument is rather pointless - externalizing warfare to poor nations and then saying the world is "peaceful" is quite immoral.

Do you have a better, moral way to reduce war fatalities?

Do you have an argument that isn't a straw-man?

Espionage is not used by governments to maintain peace and reduce war fatalities - it's used by governments to gain an edge over their adversaries. Espionage existed in WW2 as it did in times of peace - to say peace is a consequence of it is absurd.

MAD is the only thing that has prevented major world conflict.

There was no WW3, however, it certainly was not peaceful. See Vietnam and the various coups in South America for example.

Then why are so many people losing their minds, banging war drums every time someone blames China in some hack or other?

Is it due to a poor public understanding of realpolitik?

It's because China is becoming near peer and it unsettles people.