Trouble is we were pathetically inept at "protecting the vulnerable" given the huge numbers of people who caught it in hospitals and care homes, which in theory should be "safe" places. If the vulnerable aren't safe in care settings, then it's impossible to "protect the vulnerable". We need a wholesale re think of how care homes and hospitals are built/operated if we're going to go down the route of locking up the vulnerable for a year or two whilst everyone else acquires herd immunity.
I'd agree we certainly haven't done a good job there. I'd expect that if we'd put some of the resources we've thrown at furlough etc. into that instead, we could have done rather better.
However, even if it isn't possible, then all we've done via lockdowns etc. is spread out the amount of time the vulnerable can catch it, and because people move from 'could cope with getting the virus' to 'too vulnerable to get the virus' all the time, through old age etc., that means we've exposed more people at that vulnerable stage. So we've probably killed more people than if we'd just gone for herd immunity to begin with.