I have never bought into the idea that delaying SS is a 6-8% "return". At best, it grows based on COLA only. A return implies that the asset grows each year and at any point in time, the full amount, principal plus growth is available for you or your heirs to use. And while different than investment risks, there are also downside risks to SS amounts as well in the future (100% taxation for example) .
Delaying SS would be better characterized as a 6-8% increase in monthly payment amount, not growth of an asset. And when you consider smaller monthly payments over a longer time vs. larger monthly payment over a shorter time, then the cross over point is around 11-13 years. So, taking SS at age 70 means there is no financial gain til at least age 81. And the percentage gain compared to taking SS early will be very low even at life expectancy of around 85 yrs.
This is just my view, but I took SS early (since I have no control over changes in SS or yearly COLA) and maximized investment assets that I at least have some possibility of adapting to market changes.