Of course, Castro didn't want to take too many risks and therefore he sacrificed Mane to be replaced rather than having to cause problems with Cristiano. I hope that in the next match Cristiano will sometimes realize that the team's victory is above all else.
It should be that all players are wise. Logically, Mane is 31 years younger. He has better stamina than Ronaldo. It should be possible to replace Ronaldo is the right decision. Castro could replace Ronaldo with a defensive midfielder or defender and push Mane forward. This can be done to take advantage of the counterattack. In addition, they strengthened the defense. Losing 2 points is quite meaningful. With the condition that the difference in points is not much. Indeed, managing Star Players will be more difficult and it becomes Castro's burden.
Better stamina than Ronaldo? I would bet if they had to pass a fitness test that most of the time Ronaldo would be the one who comes out on top. I think even the toughest haters of Ronaldo have to admit that his physical condition is insane for a guy at the age of 38. His stamina is not to be confused with his top speed although I think that he would still be faster than Mane as well. But his stamina is probably better than 90% of the players in the Saudi Professional League at least. But one issue for him could be the motivation and the last few percentage points in terms of performance. He is used to play against the best teams in the world in front of the best fans in the world. It could lead to a lack of motivation when he doesn't play on that level anymore.