The Cavs lost this game when LeBron got tired, which was towards the end of the fourth quarter. When LeBron had energy, he was perfect. When he got tired, he was not. Watch the last 6 minutes of the game. A couple of turnovers, a couple of missed layups, and pass outs to teammates instead of taking it all the way to the basket. He also couldn’t get back on D fast enough.
LeBron ran out of gas. It’s as simple as that. Your point about slowing the pace is a good one — you wonder if LeBron could have saved some energy for the fourth quarter had they slowed the game down.