If there is a discussion about the three teams Manchester City, Real Madrid and PSG to secure the next round then I will be first in favor of Real Madrid that this team will definitely secure the next round. PSG are performing well and the opponents they have ahead of them may be able to overcome their hurdles and by overcoming that hurdle they will secure the next round. Now left is Manchester City, although this team lacks consistency but if all the players currently in Manchester City can play their best from their respective positions then surely Manchester City will secure the next round. Qualifying for the next round from the group stage is actually not a difficult task for the big teams but the opponents they have to face in the next round are usually tough opponents and then many big teams lose out of the competition.
I agree with you Real Madrid has a lot of experience and plays well consistently so they have good chance of making it to next round. PSG has been playing very well lately and they might be able to overcome their next challenges and move on to next round. Manchester City does not play well all the time but if all their players do their best they have enough good players to make it to next round. You are right getting out of the group stage is not that hard for big teams but teams they play next will be even tougher and that is when it gets really challenging.
Manchester City ended the season with a great performance when they won the Champions League title and they sold some key players in the transfer window at the end of the season. But despite selling key players, Manchester City performed well again the following season and secured the Premier League title. But this season they are not doing well at all. The current team is not much different from the team Manchester City was last season but we can see only a change in performance. Real Madrid was strong and still is strong but they have had many key players injured together and their injury problems have affected their good performances so badly this season.
I think Real Madrid will solve their problem but if Manchester City don't bring new players into their team they may not solve this problem.