That paper doesn't actually shows that its the lockdown that responsible for the decline. Its the classic correlation does not necessarily mean causation.
Who says doing nothing ? There are lot of thing that can be done : vaccine research, method of treatment improvement, promote hygiene, increase medical capacity (if needed), etc
The economy is going down the shitter no matter what. Might as well make it temporary instead of permanent (which is exactly what's gonna happen if "1%" of the entire world dies, and many more get severely injured due to COVID complications).