We do know the answer. Lockdown achieved significantly less cases and deaths than would otherwise have happened had we not locked down.
Of course it worked, but it caused enormous issues for people and there is no justification for another one. Not in a highly vaccinated society. And there will always be a spike when you unlock because covid is here for the long term and cannot be eradicated.
You can;t keep locking down forever because there is more to life than covid. I cannot support another lockdown and it would be disastrous.