France, Germany, Canada, US, Australia... many or all of the most advanced western nations have positive avg gdp around 1.5 to 2% and positive population growth as well. These are not the primary factors behind failing pension systems. In nearly all cases it ends up that those in charge dont make the required payments. In my home state that is the issue: had the mandated payments been made there would be no crisis. The state broke its own contract and dissobeyed a court order to fund unrelated discretionary spending. The major private pension failures have been similarly aflicted, executive flee a bankrupt company with agregate golden parachutes measured in hundreds of millions but the pension fund was ignored with underpayments for decades.
Our retirement systems are broken, and part of it stems from their own excessive costs, but there is no sinhle cause here, its a complex issue with complex causes, and shifting demographics and economic growth are only very minor factors. Bad policy, cynical politics and budget shenanigans, self interested executives, and simple incompetence and hobest mistakes all play the bigger part.