Your last paragraph is my point exactly. I agree we had to lock down because we didn't do anything else. Upto and after the first lockdown there still wasn't a mask mandate, social distancing or enforced hand sanitization.
Would we have had to lockdown if these measures had been brought in and enforced? I don't know. It is likely that a short sharp lockdown may have been required from time to time, a 2 week covid break, so to speak. But, as I say, I don't know, and we have no way of knowing, other than looking at otherr nations who went down that path, comparable or not.
My initial point was that lockdown was necessary, isn't a fact. Lockdown became necessary, that is a fact, of course.