An idea to help solve the uselessness of 90% of the 5* champs ... Give Adrenaline rush to the 5*s, &
something slightly more innovative and powerful to the 6*s.
Imagine having Adrenaline rush for the 5*s. I wouldn''t mind ranking to 3 a 5* unduped Hulkbuster if he had Adrenaline, or heck even an unduped 5* Kamala Khan.
Then for the 6*s, since 95% of the ones in the non featured pool are useless as well, give them something better than adrenaline rush.