It’s not ‘so fast’ as it’s kind of normal for players rankings to boost after winning championships, MVP, FMVP etc.
take the example of Dirk Nowitzki. If you take out that 2011 season, where does Dirk rank all time? Top 50? That one single season in 2011 where he went on an incredible run beating Kobe’s Lakers, OKC Big 3, and Lebron’s Heatles boosted him from top 50 to top 25 all time. That’s a HUGE boost just from one season.
So for Lebron the thing is, by 2010, he was ranked in the top 20 by guys like Bill Simmons in his Book of Basketball. That was before Lebron won any rings.
When Lebron won his first ring in 2012 and his third MVP I would say that equals Moses Malone (1 ring 1 FMVP 3 MVPs) and Moses is a top 15 all time player. So by 2012, he was already at Moses’s level.
When Lebron won his second ring in 2013, his fourth MVP, and had an incredible season – 27 game winning streak, 1st team All NBA, 1st team All Def, 2nd in DPOY voting, beating a great Spurs team in a tough 7 game series, and his 2nd FMVP – is when he vaulted into the top 10 all time.
Then in 2016.. this is the big one. He led a Cavs team that were considered contenders but still underdogs to win the championship against a 73 win team with the unanimous MVP on it coming back from 3–1 down. He had back to back 41pt games, followed by a Game 7 where he had one of the most famous blocks of all time and a 27pt triple double and led both teams in every statistical category. That 2016 ring boosted him to top 3–5 all time for most people and that’s when he entered the GOAT convo.
The 2020 ring, which a lot of Lebron haters dislike because he played in the bubble, only adds to his top 3 and GOAT credentials.
For me, in terms of greatness I had it like this..
2010: Lebron is a top 20 player. He’s still below Moses, Dr J, Hakeem but he’s around the same level as Baylor, Barry, Karl Malone, KG and Havlicek for me.
2012: Lebron is a top 15 player. He’s about the same level as Moses but still below Hakeem, West, Oscar, Kobe, Dr J, Shaq etc
2013: Lebron is a top 10 player. He’s ahead of Hakeem, Shaq, West, Dr J, Oscar and around same level as Bird and Kobe. Still below Duncan and Magic though.
2016: Lebron is a top 5 player. He’s ahead of everyone except for MJ, Wilt, Kareem, Russell for me.
2020: Lebron is a top 3 player. He’s about the same level as Kareem for me right now and is only definitively below MJ and ahead of everyone else.