My understanding is that herd immunity can be seen differently for different things. As such, it gets really tricky really quickly, as some folks will be talking about the kind of immunity you can have for things like Measles, while others will be talking about Flu and such.

That is to say, a whole shit ton of talking past each other.

My own view is that looking at population level metrics usually means that you can't really view the individual level metrics at the same time. Way too easy to see confounding increases in personal risks from some protection that oddly leads to more damage at the population level.