You're right madrid is the only team that was able to win the champions League trophy back to back some few years ago and since after then no team has been able to repeat that fit so it will be very difficult for PSG to repeat what they did last season but let she how long they can go in the champions League this season before they can be eliminated if possible by any other team
Allow me be the early judge, PSG cannot win Champions League again, i mean consecutively after winning last season. PSG performance isn't consistent as it was last season, their chances of winning back to back Champions league title is very slim, when i watch other teams i feel they are more prepared especially from Premier League, if it doesn't go to La Liga then any of the Premier League team wins.
Madrid also don't display a strong likely performance of winning the Champions League, they lack what it takes, Barcelona are a more suitable competitor for the title than Madrid, it will take them sometime before returning back to previous success like consecutively winning the Champions League.