the US was not mostly locked down, and indeed made noncompliance with safety measures a major partisan identity issue for the faction controlling the federal executive, the upper federal legislative house, most state governments, and much of law enforcement even in the other states. It mostly had modest, inconsistent, uncoordinated, and largely unenforced restrictions. A few jurisdictions did at least nominal lockdowns for fairly brief periods (California did twice, though virtually every county sheriff had publicly announced that they either would not enforce orders at all or would do so only by education around compliance by the time of the second one near the end of 2020.)
They failed to actually achieve 'herd immunity' and did not avoid the eventual virus death toll:
https://www.news.com.au/world/coronavirus/global/sweden-cris...
By comparison Finland, it's neighbor took a much stricter approach and never reached the same level of death.
Finland: 931 deaths at 168 per million with a 1.0% death rate.
https://epidemic-stats.com/coronavirus/finland
Sweden: 14275 deaths at 1406 per million with a 1.4% death rate.
Sweden: https://tradingeconomics.com/sweden/gdp-growth-annual
Finland: https://tradingeconomics.com/finland/gdp-growth-annual
Looking at those charts they show very similar economic outcomes for the two countries.
Of the last 4 COVID effected quarters Finland won two and Sweden won two.
And Sweden actually felt the highest quarterly contraction at -7.7% compare to the -6.1% for Finland.
That 0.4% difference suggests Finland's health system was better than Sweden's at handling the virus, as your chances of dying were much less.
When it comes to actual deaths Finland was doing over 830% better (i.e. 168 per million compared to 1406 per million) than Sweden.
Edit: Fixed my bad math. My 90% better figure was out by a factor close to 100.
[1] https://www.economist.com/graphic-detail/coronavirus-excess-...