I thought the same like you but.......
Lets say you have 6 star players even 7 star 
It's ok to keep low rating players because  the cup fix match 
My team is 67.5 for the next season I will get teams the same rating as mine so it will be lvl 12-13
And I will be next season lvl 10
This season in the cup I beat teams lvl 11 
Meaning high star players mixed with low star rating players  
Will give u fair chance in the cup fixture for next season. 
That's the problem with cup fixing sometimes thy give you higher rating teams because of 
The rating system.  
After season start he can sell players and he won't lose much 
It's batter to get fair matches then unfair matches 
Next season I probably get higher team lvl' then me 
Because I don't have low rating players this season 
As you can see. 
