> Germany both went through massive austerity in the 1990's to re-tool their economies from massive debt overhang - and it worked.

AFAIK, for Germany that was mostly consequences of reunification. Economic growth slowed in the early 2000s and the centre left instituted the Harz benefit reforms etc. They certainly didn't pay down goverment debt in the 1990s: https://tradingeconomics.com/germany/government-debt-to-gdp