The main problem wasn't the 100m we paid him. Paying that astronomical salary severely taking Juve down.
There were a lot of different reasons for our downfall, but the main one imo were the choices we made in midfield, starting in the summer of 2019, but especially from 2020 onwards.
Even though it wasn't even close in quality to the 2012-2015 midfield, Matuidi-Pjanic-Khedira was quality and a very balanced midfield that won a lot.
We replaced them with players who were either bad, not good enough, mental midgets, or injured a lot (Arthur, McKennie, Bentancur, Ramsey, Rabiot). All the attempts to fix these mistakes were futile. Locatelli didn't live up to the expectations, while Zakaria, Paredes, Pogba v.2, Alcaraz and the kids were just average or seriously bad. Last summer we made two more mistakes with Douglas Luiz and Koopmeiners. One quality midfielder in 5 summers (Thuram) was just not good enough and that is why we are where we are.