I suppose I agree more with you than before, but I still think that aside from the fact that a manager or tech lead is ostensibly used to hearing people be angry (or frustrated, or whatever) -- why is John's boss more deserving of "You screwed up." than the person who dropped them? Yeah, obviously, the prod tables shouldn't have been droppable. John still shouldn't have dropped them. In fact, John, the original developer who implemented them, anyone who altered them since, the tech lead, manager, and frankly anyone who knew this data was critical could have all raised the alarm.

Ideally a blameless post mortem allows the freedom to identify any of the potential fixes that could've stopped this, and empowers anyone who could've dealt with it to deal with future issues. If you blame the manager then that can implicitly absolve everyone else in the chain.

With that said, I would agree that having a primary owner of things does matter. For that reason, sure, making the manager more aware might help in future. I still think it's a bad idea for org culture though because many managers will respond to "You screwed up." with trying to ensure future blameables find their way to another target. Instead, I'd prefer approaching the manager with "We could've caught this in [any of the ways we could've caught it].", and if the manager doesn't care at that point they're just fully incompetent.