Real Madrid even have a very brilliant reserve team and why they are yet to effectively put that to use is another things really don't understand and do bother about sometimes, I think it will even be better if they can rest some of this bigger players awhile like they did last season and allow the reserves to play few games as the key players are stressed already, they have the stress from their club side and Still gets almost same from their country sides too when the needs arises so I believe they will get fatigue and injury prone so it will be ideal they are rested at some instance.
When the match schedule is too busy for a player, usually the coach will also make appropriate player rotations by limiting playing time so that it is not full time for a player. And yes, sometimes playing several second tier players is the right thing to do if the opponent you are facing is not a very strong team. But when the opponent you are facing is a strong opponent, you still have to play the main player and only use reserve players when needed, such as when the main player looks tired. And yes, Real Madrid has good second tier players and their quality is no less good than the main squad, but the problem is that sometimes they lack playing experience and giving them time to play would be very good for their experience on the field, especially for young players.