It should be like that in a team, but there are some players who do make a big contribution and their contribution cannot be replaced, such as Kane in Bayern's front line now, even though there are reserve players to replace him, when Kane is absent, the team will experience a little difficulty and that also applies to almost all teams where there will definitely be mainstay players in a team.
Players who can always be relied on will not always be on the field without getting injured and that is why each team does not only rely on 1 player who contributes the most in the front line because if they do not have a reserve player who has almost the same strength, the club will experience a decline, especially since we also do not know what bad things will happen in the future, sometimes there are players who suffer serious injuries so they are forced to be absent for a full season, therefore, to avoid something that is not desired, the coach must be able to anticipate this.
This is one of the worst scenarios that many teams face. The star player of the team gets injured and doesn't get a chance to play for a few months, then the performance of that team decreases and it can't be a competitive team like before. Actually, there are very good football players in every team, but since these players don't get enough game time, their stars don't shine, and after an injury or something similar happens, they feel a lot of pressure on themselves and can't actually perform as they should