I don't agree with that argument. Did Garnett become Scottie Pippen by going to Boston? No, he's still considered one of the greatest power forwards of all time. Gilbert never brought him his Pippen to win championships so he had to go seek out players himself. Even if you're one of the greatest of all time, you're not enough to win a championship.
The pieces were in place for him to lead Chicago for a legit run at a championship, which would have cemented his legacy regardless of how many titles he ended up with. Instead, he chose to run to arguably the 2nd or 3rd best player in the league - who unlike LeBron has already shown he can lead a flawed team to a championship - in a scheme to create some bogus Yankee-like superpower. Unlike Jordan, Bird, Magic or Kobe, LeBron's mental toughness and ability to lead will always be question in now, which for now ends the conversation about him potentially being the greatest.
Also, Boston's big 3 were all in the late stages of their careers and complemented each other well, which I don't think is comparable to frontloading a team with three top guys in their primes.