LeBron is mostly handicapped by himself. When you consider his talent, he had the team to beat the Spurs both those years, and was a lucky play away from losing in both finals.
His problem is that he's a stat padder and a frontrunner. This might sound crazy, but he literally caps himself out at a certain stat line -- especially when he's getting his ass handed to him. Last year's finals is a great example of this. He'd put up all his numbers in spurts, usually in the first half, and disappear in large chunks of the games. This is why despite having better numbers, he was being outplayed by Kawhi Leonard at several points in the series.
Sometimes he just needs to take over and score 40 or 50, but he's not willing to do it or even try it. Instead he'll hide in his point guard shell and go for that 'efficient' near-triple-double line and stop there.
