You have said it all. Inter underestimated PSG due to a lot of reasons. Firstly, they haven't win the trophy before and don't have the finals experience. Secondly, they struggled till they got to the finals and lastly, Inter defeated Barcelona who everyone sees as the best last season. I believe that Inter didn't even prepared properly for that finals. Assuming, they prepared for the finals the way they prepared when they played Barcelona, PSG wouldn't have humiliated them that way.
I hope Inter can learn a lot from last season's defeat, but seeing Inter current condition, which is even worse, makes them even less likely to succeed in the Champions League. Meanwhile PSG is getting stronger, so now the Champions League group stage presents many tough opponents for PSG to face, such as Bayern Munich, Barcelona, Leverkusen, Atalanta, Tottenham, and even Newcastle. All of these matches will be extraordinary challenges as PSG begins its journey.