Do you realize that Lebron scored 27 points and grabbed 19 rebounds in Game 6? Also had 10 assists (with 9 turnovers, which tells me he was trying too hard).
The only game where you can call him out is Game 5, and even if he played perfectly, the Cavs still lose that game. Did you ever stop to think that maybe the Celtics defense was just that good and broke his will for that particular game?
And a player having their will broken for one game, or even a series, has happened to every great to ever play. Magic against the Celtics, Jordan against the Pistons, Shaq against the Spurs (or Rockets), Duncan against the Lakers, Kobe against the Pistons and Celtics.