Aside from Ewing > Robinson, I also had trouble with a few of the rankings.
Shaq > Hakeem. Shaq was great, really great, but I would take Hakeem over Shaq all day, especially considering Hakeem's defense.
How the flying did Parish got ranked so high? He ran the floor well, great. But > Walton, Reed Hayes and Thurmond? GTFO! To me, Parish was clearly the least of that group.
Thurmond once again got underrated. Although I am more familiar with him when he was way past his prime, his quickness and defense even after his prime was enough to convince me that, during his prime, he was a lot better than people gave him credit for.
Walton was great, could have been top 5, too bad for injuries. Very much like Yao's career, but much much better. Walton was the best passer out of all big men, great defensively, extremely high IQ basketball player (not sure why he is such a horrible commentator though), can score when he wanted to. I would have loved to see him, KAJ and Moses fighting against each other uninjured and during their primes.
Moses was way underrated, once again. He dominated, and I mean dominated KAJ. Sure KAJ wasn't at his absolute peak, but Moses just straight out abused him. Also, greatest offensive rebounder of all time. Not as great defensively, as say Hakeem or Robinson, and could be a black hole at times, but the dominance he had in the middle was only bettered by Shaq and Wilt.
Overall, that was a pretty damn bad list.
I had them ranked as:
1. K. Abdul-Jabbar
2.Moses Malone
3.Wilt Chamberlain (haven't really witnessed his prime, tbh)
4.Hakeem Olajuwon
5.Shaquille O'Neal
6.David Robinson
7.Patrick Ewing
8.Bill Russell (haven't seen him in his prime, but honestly, if I were to go with stats and les, he would be top 5, no question)
9.Bill Walton
10.Nate Thurmond
11.George Mikan (haven't seen him at all)
12.Wes Unseld (again, past his prime)
13.Elvin Hayes (memory hazy, tbh)
14.Willis Reed (again, one of the more overrated guys because he played for NY. Fantastic leader, great tough guy, great mid range game, great passer, but his impact of the game was over credited at the expense of their backcourt).
15.Robert Parish (really, how the would he be here, I would put Mourning, or even Brad Daugherty in his place. I mean, come on, clear 3rd option, never led any teams. He was never the best player on his team, or even 2nd best, how the could he be ranked in the top 15 centers of all time?)