we should get used to these matches as well as the play offs, the new champions league has a totally different format from the old champions league until last year. from this year whoever places between 9th and 24th in the standings will have to go through the play offs and you can also meet 2 big teams as happened with real madrid vs manchester city. also to consider the fact that the winner of real madrid - man city will find a team between Leverkusen and atletico madrid in the round of 16, so another fairly competitive match
All of those possibilities can happen this season and now we have seen that Real Madrid will face Manchester City in the play-off round. Many people regret this meeting because it is considered too early for a big match like that to happen in the play-off round. But we all can't do anything because the draw says so. Also as you said, after they play in the play-off round, there are many possibilities for big matches to happen again in the round of 16 later. I mean a match like the meeting between Real Madrid and Manchester City could happen later.