I disagree with that. LeBron is obviously the best player in the league, and when he's on his game, he's virtually unstoppable. But one man doesn't win a championship in the NBA. Even Jordan had Pippen (and Grant and Rodman and Kerr, etc.). Without Bosh, Miami was taken to 7 games by a Boston team that's well past their prime. He's not in the same class as Wade or LeBron, but he's still an All-star, he still can knock down shots, and he gets you boards and extra posessions. LeBron can't win a championship on his own; we saw that several years in Cleveland where he leads his team to dominate the regular season but they can't come through in the playoffs because one man can't play against five by himself.
So, yes, LeBron is the most important. But you need Wade and Bosh if you're trying to win a championship with such a sharp drop off in talent after those three. Seriously, Battier or Chalmers as the fourth best player on a championship team? The lack of depth in Miami is disturbing, and getting rid of Wade or Bosh compounds the issue.