There are ways you can fix this mess Kabam
95% of players don't want 6*s. It nerfs rosters because of challenger rating.
But there's a way you can fix this.
Remove challenger rating altogether...
or....
Delay 6*s for a year and introduce them at an appropriate time. An appropriate time is when a reasonable part of the playerbase has easy access to rank 5 4*s and an acceptable access to rank 5 5*.
This means you need to do the following:
T4Bs, T4Cs, and T1As are rare. Make them a lot more common. This will allow more players to rank 5 their 4*s.
Increase T2A access more. Not as much as T4Bs/T4Cs, but enough to where a reasonable percentage can rank 5 their 5*s.
When enough people have rank 5 4*s and rank 5 5*s, then you start introducing 6*s.
You're 12-15 months too early. Progression can't be forced. Your average player has a ton of rank 4 4*s that they can't rank up and most players even in solid alliances have a dozen unduped 5*s at rank 2 because there's few worthy to r3 or r4.
You can't force sudden change in 4 months.