Comparing COVID19 deadliness to "the flu" or "the common cold" is apples to oranges. The latter two are collections of viruses. Moreover, humans are resistant to the latter through longstanding herd exposure. COVID19 is nontrivially immuno-novel to humans due to its zoonotic origin.
COVID19 isn't very lethal. However, its r0 can overwhelm hospitals. Delaying it gives time to improve treatment. The main purpose of this is not to give the elderly and unhealthy a few more years of unproductive life, but to mitigate the damage to those who would otherwise be productive for many years.
COVID19 doesn't just pick off the weak; it damages the susceptible. The goal is to allow the latter to develop antibodies at minimal cost.
Government-mandated lockdowns are only "necessary" where the alternative is chaotic revolution. Epidemics of sufficient severity cause voluntary lockdown anyway, via individual choice.
There is nothing wrong with a local government mandating lockdown. However, a central government's primary job is controlling its borders: people, pathogens and packages. It needn't concern itself with the interior affairs of provinces. A lax province will find itself blacklisted by neighbors anyway.
Unfortunately, many central governments failed to do their jobs by locking down their borders, and then covered their mistake by locking down the interior population instead.
Epidemic naturally restores subsidiarity. Central lockdown inhibits this, and is therefore bad. The idiotic spectacle of government agents chasing down lone men in nature speaks for itself. As the Native Americans learned, disease is both the vanguard of servilization and the reaper of declining empires.