I will grant you these seven:
1. Kareem
2. Russell
3. Wilt
4. Shaq
5. Hakeem
6. Moses
7. Mikan
The only other guys I could plausibly see ahead of Joker are Walton & Robinson, but that feels like we're stretching it. And he's definitely passed Willis, Unseld, Ewing, McAdoo & Cowens.
I would list them:
1) Russell - best player on most dominant team in NBA history
2) Wilt - Would have won a lot of titles if not for Russell (and booze and women).
3) Kareem - I like Kareem, but he would occasionally underperform against other top centers of his era, like Moses and the Chief.
4) Hakeem - great player on both ends, and he tuned up some of the best players in NBA history (Shaq, Admiral, Ewing) head-to-head.
5) Shaq - great player, but didn't have range and showed up every fall completely out of shape.
6) Moses Malone - He was a great player on both ends of the court and the best rebounder I can remember.
7) Ewing - People remember the goofy stuff and the Knicks playoff collapses, but Ewing had a great career.
8) Robinson - People forget his greatness because of how humble he was and his aversion to self-promotion. Great defender that adjusted his game late in his career to enable Duncan's first title.
9) Jokic - Incredible offensive player, probably Top 3 on this list offensively. Not nearly the defender that some of these other players were in their prime, though. That said, I expect Jokic to make it to #7 or #6 on this list by the time he is done.
My "what could have been" list for centers:
1) Arvydas Sabonis - May have been the best center of all time, and Portland would have won 4 or 5 titles if he had arrived in 1988 when he was supposed to. By the time he got to the NBA his knees were shot and the hard living was catching up to him. He was still fun to watch.
2) Alonzo Mourning - As good as Robinson defensively, and a very efficient offensive player too. His body betrayed him, he went to a minutes restriction and was a shadow of the player he could have been.
3) Bill Walton - Not caring about his body caught up to him early in his career.