To be considered the best ever you need to be a ... great offensive player, great defender, great leader, great winner.
Magic : Zero defense, not much of a scorer, but the best passer of all time
Russell : Not enough offense, best big man defender of all time though
Jabbar : Was a monstrous player in his youth, but didn't win as much then. Team success came steadily only when he was one weapon on a team of many weapons (Magic, KAJ, Worthy all won Finals MVPs in the Showtime era)
Oscar : Similar to Jabbar. He had awesome talent, but didn't win till he played with Jabbar.
Bird : Can be rated along with the above, he too played on stacked teams, and didn't shoulder as much of the offensive load, but was clutch as .
Only Jordan and Wilt score high on all those categories. Wilt was obviously a statistical monster in his early days, but declined (maybe by choice) to be the main scoring option in his later Laker days. And he had only 2 'ships to his name.
Michael Jordan is the only player to have a complete resume on all fronts:
A. Offense:
Highest career PPG average, 10 scoring les, 5-time MVP, 10 All-NBA first team selections
B. Defense:
DPOY, 9 All-defensive first team selections
C. Winning:
6 championships with 2 three-peats, Finals MVP in all 6, 2 Olympic gold medals
D. Leadership:
The go-to guy on 6 championship teams, the anchor on both offense and defense, the guy who took and made numerous clutch shots under pressure.
Put the achievements of all the others in these 4 categories, you'll find that all of them lack something or the other. Only MJ had it all.