Actually that's interesting, I want to watch Manchester City play without De Bruyne, Rodri and Silva, also Real Madrid play without Bellingham, Vinicius and Valverde. So this could make other teams can win against both of them, unlike people who're predict the winner would be either Real Madrid or Manchester City.
I would rather watch championship league instead of watching those clubs to play without their best players. Even though their secondary squads are probably equal compared to the main squad but it's not what the public wanted to see. Football follows the demands of the viewers.
You seem to have hoped for something that will never come true, but I have seen that City played without Bruyne and Silva. It was only because of the absence of Rodri, who was not injured at that time.
An entertaining game is when each team shows the maximum performance, so in fact we have often seen the matter of playing without the best players, but there is no reason for the coach to reserve them if the player condition is very supportive. For me regarding the Man City match against Madrid, they must have been prepared with the best squad. Seeing the condition of each team that will play in the UCL is currently showing changes, and I am sure that Man City and Madrid will field their best players in Leg 1, because the target is big enough to secure points. This is just a matter of tactics and however player rotation will be carried out. Believe it or not, UCL is a match that will be the most important treat not only for us as spectators but for the reputation of a team.