From the results of the group stage I believe the big teams will up their games and stop underestimating the underdog teams that has proven most of them wrong. PSG started the competition defeating ATM by 4:0, a result that by right made the rest of the teams to be careful of them but watching them fail to grab an easy win against an underdog team shows thwt they are becoming too tired as they have been faced with a lot of competition. The next phase of the competition will see the teams becoming more serious we will see teams that will make it to the finals soon.
The bookmakers underestimated the American teams by placing high odds, giving the impression that the level of the European teams was much higher than the level of the American teams. But the reality is showing the opposite, the American teams are stronger than the European teams.
PSG did not underestimate their opponents, they lost even though they played with their good players. Of course, the lack of some players could have created a different atmosphere, but it would not guarantee that PSG would come out on top in this game.