Fukushima was neglect. As you said we had known those types of tsunamis were possible since 1972, but no additional safety measures were put into place over the decades.

There were multiple studies and suggestions ignored a decade before the incident: https://en.wikipedia.org/wiki/Fukushima_nuclear_disaster#200...

It wasn't that there was a fundamental flaw with the design, just the sea walls needed to be higher.