If killing is the goal yeah it's a shit weapon, but what if it's not about killing and its about containing and stopping or slowing down Chinas economic growth. Probably assumed China would be able to contain it like Sars and the damage be mostly regional. Don't forgot they want to keep the chinese market healthy enough so they can exploit it.The deliberately engineered bioweapon theory doesn't make sense because high contagiousness with very low mortality means the pandemic can spread rapidly cross borders, including back to US and US allies.
Ideally, an bioweapon would have a low-moderate contagiousness, and high mortality rate, and high affinity to East Asian DNA genetics, so it can largely be contained within China or East Asia boundaries.
With COVID-19, you have a weak mortality rate and greater affinity for Americans and Europeans than Chinese both in terms of infection and economic damage. What a epic failed bioweapon attack.
By unleashing this virus it would buy the West a couple of more years to finish up Ukraine and Russia and further prepare the pacific theater...
If it weren't for all those mask off moments the last 2~3 years I wouldn't have thought the west would be able use biological weapons.