How devastating a nuclear blast can be in a major city?

A fictional simulation of a nuclear blast illustrates the danger of a nuclear blast.
Are we prepared for a nuclear attack? Of course, the world we live in is much safer than in The Cold War times but do we have enough knowledge on how to protect ourselves. In this Youtube video, the documentary filmmaker Neil Halloran presents a simulation of a nuclear blast in an average midsized city. He works in collaboration with the Nobel Peace Prize Institute - Research and Information in order to tally the estimated deaths.
Neil is conducting a purely mathematical experiment. His initial point is the assumption that today we possess much more powerful weapons than the ones used 60 years ago in Hiroshima. Let’s assume the bomb is with 500 kilotons of nuclear power which means that within an 800 meters radius around the place of the bomb drop everything and everyone will be destroyed. What is more: on a 2 km radius, no one survives. Having in mind the population density today, this equals to 120 thousand people killed.
The simulation continues explaining that the nuclear blast has the potential to hit in a radius of 11 km and cause a burn of 3rd degree on the skin. Adding the fact that not everyone will be directly exposed to the heat and fire, the number of killed on between 2 and 11 km varies from 98 % to 50 % caused by radiation smoke, building debris, radiation sickness which is nearly 500 000 people. And this is only before the radiation hits in the following couple of days.
What needs to be taken into consideration having watched this short video: even we are not afraid of bombs and there is no military education in schools, the nuclear bombs remain one of the largest military dangers in the modern world. The Cold war is over but the current US-Russia antinuclear treaty expires on February 5th, 2021.
In the 21st century, the weapon technology has also developed, and now besides the conventional and nuclear, there are ultramodern hypersonic bombs that are more difficult to be detected by the radars. The citizens and big multinational organizations should consider the risk by following the already known international treaties and continuing to reduce the number of countries having nuclear bombs; to keep reducing the Cold War arsenals, and also take care of nations pledge not to strike unless attacked. And this nightmare simulation never becomes a reality.