Sakin winning a championship does not solely define the greatness of a player. But it does enhance a player's greatness. There are note-worthy players who have won only 1 championship in their careers but are considered one of the greatest players ever. Jerry West only won one. But not winning multiple rings does not deter how great he was as a player. He is the NBA logo alone tells you how great he is. Oscar Robetson is another. Won only one. But try to come up with even one player who can average a triple double in a season let alone almost a career.
While championships cements your greatness, it does not define a great player. John Stockton who never won a ring I consider the 2nd best PG of all time. His assist and steals record as it is seem untouchable. Last time I checked, I believe Jason Kidd is second but close to 4,000 behind. And with his career winding down, won't overtake Stockton. Among active players, Nash is still about 5,000 away. Won't get there either. As for steals, Stockton is still ahead of Kidd by about 600. Among active players, next is Kobe behind about 1,400. So nobody is breaking both records. Is Stockton a great player. I believe he is. Does not winning a championship deprive him of the accolade of being a great player. No it doesn't. But it would have enhanced the resume of an already great player.
Truth be told, anybody given the right situation can win a ring....Jack Haley, Mengke Bateer, DJ Mbenga, Earl Cureton, Chuck Nevitt, Adam Morrison, etc. But not anybody can just win 3 MVPs, be All Time leaders in statistical categories, average a triple double in a season or even be the model of the NBA's logo. Record holders like Stockton, 3-time MVPs, triple-double average for a season players cannot be overshadowed by not winning a championship or winning just 1 ring.