Yes, in the presence of rational actors this would be avoided, but here we are anyway. A single nuclear strike would be met with retaliation and it would escalate to mutually assured destruction like clockwork. A lot of optimists thought Putin would not invade Ukraine because of the risk and that he was posturing. It would be similarly optimistic to presume rational actor decision processes. That may be a strategy he is employing, but we will never know until the brink. We are on the knife's edge of disaster here.