The EU countries don't need 8+% returns to provide their citizens with comfortable retirements. One major reason is that in the US you need to save for living to an age much greater than the average life expectancy.
That's only as sustainable as demographic trends and economic success allows.
In New York State, the pubic employee fund is arguably fully funded, and most employees are eligible to retire at 55 with 2/3 of their salary as a pension. That fund requires a 7% annual return to avoid additional employer contributions.
Those EU countries don't need to achieve 7% annual returns because they won't pay as much as 2/3, nor allow retirement as soon as age 55. Their models are much more sustainable.
It's going to get interesting in the US, as an increasing percentage of private sector retirees are scraping by on an average $1K a month whilst public sector retirees are enjoying cruises and taxes are being raised (or services reduced) to fund them.
In New York State, the pubic employee fund is arguably fully funded, and most employees are eligible to retire at 55 with 2/3 of their salary as a pension. That fund requires a 7% annual return to avoid additional employer contributions.