70% is enough for the original Covid. Covid moved the goalposts to Delta which needs different numbers. This is not experts moving the goalposts, this is Covid changing on us - as was always expected to happen and why experts said we don't know what % is required until Israel showed 70% was enough for the original Covid strain.

Herd immunity happens when a disease can't spread because all people surrounding the infected person have enough immediate immunity to stifle its progress. Delta seems to be able to spread to people in the gap before the immune system recognises it, so it may be something that can't be stopped by herd immunity.

Other models are certainly possible, but only work in places where people have higher trust in their government, and think about collective welfare over their own individual selfishness. Unfortunately, people in the US (and much of the West) care too much about "mah lib-ur-tee" than doing their part to help keep their neighbors healthy.

Also I think your focus on Japan is a little weird; they went through their own bad time with COVID, and even consider the recent case of the large flare-ups surrounding the Olympics.