I don't think the big three can maintain the energy level at 40 minutes a game. Two years ago they could, and they might be able to once or twice in a seven game series, but if asked to do it on a consistent basis will wear down, and not be able to make stops in the 4th quarter.
Even though this is the playoffs, and there are days off, it's still a grind, and will begin to take its toll in the Cleveland series. With older guys the law of diminishing returns sets in.
I still think this year's team plays best when a lot of guys play a lot of minutes.