Death per million inhabitants in these 4 countries: https://ourworldindata.org/explorers/coronavirus-data-explor...

You can also compare with other neighbors and Europe: https://ourworldindata.org/explorers/coronavirus-data-explor...

Seems like a minuscule percentage.

Is that a pragmatic-enough reason to significantly deteriorate the economy and mental health of the enormous majority of people?

The GDP change in 2020 for Sweden, Norway, Denmark and Finland were -2.8%, -0.8%, -2.7% and -2.8%, respectively.

Sweden had no advantage over its neighbors on the economic outcome, and you'd need to cite real data in order to make an argument for mental health. Naïvely assuming a causal relationship with quarantine measures for both without considering positive effects of better health outcomes (and other factors) is fallacious.

You can view JHU's raw data sources at https://github.com/CSSEGISandData/COVID-19. According to that, they are getting COVID death numbers for Sweden from the Swedish Public Health Agency via https://experience.arcgis.com/experience/09f821667ce64bf7be6.... I am not fluent in Swedish, but perhaps someone who is can tell you exactly how the Swedish Public Health Agency measures them. Likewise for the other countries cited.