>500 vs 3000 is kind of irrelevant when you could already kill millions upon millions.
No, it's not. The reason for having thousands of warheads is not to blanket the earth in a nuclear apocalypse. It's to have enough failsafe and fallbacks that you are guaranteed to destroy the opposing force's arsenal before they can hit you. 5 missiles at once can be trivially intercepted. 500 missiles at once is unstoppable. The first exchanges in a nuclear salvo would be aimed directly at each other's silos. The vast majority of research in nuclear weapons today is in penetration capability of hardened targets (which systems like the UK's Trident do not possess) not widespread killing of civilians, and whoever maintains a superior capability in this respect will have the upper hand in any negotiation.
No, it's not. The reason for having thousands of warheads is not to blanket the earth in a nuclear apocalypse. It's to have enough failsafe and fallbacks that you are guaranteed to destroy the opposing force's arsenal before they can hit you. 5 missiles at once can be trivially intercepted. 500 missiles at once is unstoppable. The first exchanges in a nuclear salvo would be aimed directly at each other's silos. The vast majority of research in nuclear weapons today is in penetration capability of hardened targets (which systems like the UK's Trident do not possess) not widespread killing of civilians, and whoever maintains a superior capability in this respect will have the upper hand in any negotiation.