Apart from the fact that Real Madrid have a nice squad, there are other competitive teams like Liverpool that you just mentioned though i doubt their ability since Jurgen Klopp will be ending his coaching Job with the team the other clubs includes, Manchester city, Barcelona, Bayern Munich, PSG and Arsenal those are the teams with fairly good squad that can be able to compete the Champions league trophy with Real Madrid.
The Champions League is filled with competitive clubs representing other competitive leagues, so not only Real Madrid has a good squad, even several top clubs also have good players and the Champions League is quite a difficult competition, especially competition between top clubs. However, Real Madrid's experience in the Champions League can be proof of how good their performance is, which will be a tough opponent for other clubs in the Champions League. I doubt Liverpool will appear strong there even though they still have good players because we don't know whether Liverpool's new coach's abilities will be better from Jurgen Kloop.
For the other clubs you mentioned, I believe they will be tough challengers for Real Madrid, but don't forget Inter Milan, Milan, Juventus and Leverkusen, which will also be challenger clubs for Real Madrid, especially I want to see Leverkusen become an undefeated club in the league and next season he will compete in the Champions League. We'll see if this club can make it difficult for other big clubs, especially when facing Real Madrid or Manchester City, which are the strongest candidates there.