Your offense is the problem.
Beating up on bottom feeders all season doesn't show how good your offense is. Having a good record doesn't mean your offense is good.
Yes, the offense is the coaches fault. The plan was almost always getting the ball to LeBron, and then just getting out of the way, and hope he scores some points. Maybe if the Cavs lost a few more games in the regular season, but allowed for some of their other players to have to take some of the burden, they might not have been so pitiful in the ECF.
When you play the Lakers, you have to game plan for Kobe, Gasol, and Odom off the bench. When you play the Spurs, you have to game plan for Duncan, Parker, and Ginobili. When you play the Magic, you have to game plan for Howard, Shard, Turkoglu, Nelson, and Pietrus off the bench. When you play the Celtics, you have to game plan for KG, Pierce, Allen, and Rondo.
When you play the Cavaliers, you had to game plan for LeBron.
Problem for the Cavaliers is that they pretty much had one guy in LeBron trying to matchup with 4 capable players in the Magic.
Magic outmatched them in almost every way possible.