That's a weird metric (one meltdown is quite a catastrophe) and the calculation seems suspicious too. Between Chernobile and Fukushima I don't see how this could be correct.
I do find your other points more convincing, though with some "citation needed" wrt. coal.
And that's before we consider the environmental and health risks of ash ponds[2], which can (and have caused) heavy metal pollution in nearby groundwater supply. The largest industrial spill in US history happened barely a decade ago, and was an ash pond[3].
Edit: I can personally recommend "The Buffalo Creek Disaster" (ISBN 9780394723433) as a writeup by a lawyer involved in a similar coal ash accident (one that directly killed over 100 people).
[1]: https://www.pnas.org/doi/10.1073/pnas.2017936118
[2]: https://en.wikipedia.org/wiki/Ash_pond
[3]: https://en.wikipedia.org/wiki/Kingston_Fossil_Plant_coal_fly...