Comparing LeBron (or anyone, really) to Jordan or anyone else is an apples-to-oranges conversation.
Yes, Jordan was an elite player. But he only ever did it with one team: Chicago. When he tried his comeback with the Washington Wizards, it was a disaster. It's similar with Tom Brady; would he have ever been the same kind of player he was if he had left New England in his prime? We'll never know, but we do know the team that surrounded those players was the major reason behind those players' successes.
LeBron James has done something Jordan never did, and that's win championships leading two teams, Miami and Cleveland. (In that regard, Peyton Manning has a similar credit with the Colts and Broncos.) That, to me, is a greater marker of greatness than numbers alone, because it means you have to have the talent to bring the people around you up to an elite squad.
What, really, can LeBron prove at this point that he hasn't proven already? At least this time around, if he does leave, he can leave on good terms, knowing he brought a championship to his hometown. He can finish his career in Philly, or be like Brett Favre and bounce around the league for a few years, and not diminish his contribution to the game.