You are correct even before Cristiano Ronaldo came to Real Madrid as the Real Madrid team was already doing better but Cristiano Ronaldo came in to be an added advantage to the team. Kylian Mbappe is a good and experience player that can even score from any spot I believe everything team will want to have Kylian Mbappe in there team so I believe it is also an added advantage for Real Madrid having player like Kylian Mbappe in there team for they will do more better with Kylian Mbappe In that team and I also believe Kylian Mbappe will put his best to make sure he wins the UEFA champions league trophy with Real Madrid since he couldn't win it with his previous team PSG.
Before the arrival of Ronald to Madrid and during his stay was actually a very big and huge difference, I agree that Madrid was doing good just before he joined them but it was really obvious and clear how they did much better after he joined them, they had more goals and the team became much more defined than it has been before the entrance of the player. He aswell had his own fair share of experience and things he got to learn from the team which also helped his career advancement and in turn, the team benefited from his stay and got more definition and form as a team.
Just like Ronaldo, I'm sure mbappe may have his own impact he's going to have on the team too aswell and the team will have their own benefit they will be getting from having such a good striker in their team which is something most teams out there really do look forward to having in most of the cases. Winning the champions league is something Madrid Is beginning not to find difficult achieving in most cases so I believe they can still get it done once again now they have got a good striker which will be a dream come true for mbappe, such he couldn't get at PSG even with all his efforts.