After the top 8 or so players, there is a group of about 12 players you could rank as high as 9 or as low as 20. I don't think Mitchell, DeRozan, Oladipo or Russell are in that group of players though. Griffin might be.
The clearly better players off the top of my head are James, Harden, Durant, Curry, Davis, Leonard, Giannis, Jokic
Debatable: George (not debatable this year), Lilliard, Beal, Griffin, Towns, Westbrook, Simmons, Butler, Embiid,
This is off the top of my head so I'm probably forgetting people and maybe have a few on the debatable list that are debatable.
While I don't think they'll ever be as good as Kyrie, Russell and Mitchell have been very good of late. Russell's averaging 24.4 points, 7.4 assists on .458/.378/.879 shooting in 31.4 mpg over his last 28 games. Mitchell's averaging 28.4 points, 4.8 rebounds, 5.1 assists, 1.1 steal on .438/.384/.805 shooting in 35.8 mpg. Russell just turned 23 and Mitchell is still 22. It's possible one or both could take a significant leap.
While I don't think he's in the top 20, I do think Russell is one of the most underrated players in the league. He has a stink to him.