Lockdowns were just meant to be for two weeks to “flatten the curve”, remember?
They serve the exact same role they did at the start. If we'd open stadiums now the exact same thing will happen, that happened 1 year ago.
Lockdowns will continue until we either reach herd immunity naturally or through vaccines or we have a treatment/mitigation for the disease.
Your conclusions don't match reality. States like Florida have open stadiums and are fairing the same as states like California that insist on totalitarian overreach.
With the exact same density as before ?
I won't say with confidence that a short, hard, lockdown would have solved things in the us, but such approaches did work in many other nations.