As we saw this year, winning a championship is more than just having one great player. There are a wide variety of factors that go into winning the chip- coaching, organization, roster, luck of the draw with playoff match-ups, etc. One guy really can't do it all, and this has been proven time and time again with all-time greats i.e. Charles Barkley, Karl Malone, Nique, etc. that are legendary INDIVIDUAL players who just were never blessed with the circumstances to win a title.
I understand that the modern-NBA is very "star-centric", but reality is that basketball is a team-sport. When the Warriors won the title, everyone got rings, not just Iggy or Steph. Everyone from the owner to the assistant equipment manager got one, because they all contributed to the championship in some way, and they all were
important.
Ultimately, a championship is a TEAM award, not an individual one. Even "Leading a team to a championship" is not a valid measurement, not only because it's incredibly vague but also because its too dependent on the aforementioned TEAM circumstances.
The only honest way we can assess how good a player was is through individual accomplishments- individual stats and awards.