Everybody who thought the Heat were going to buzz-saw their way through the league (including myself, at least for a time) were foolish. Though basketball is about the stars, it takes a full team with depth to win consistently against decent teams.
The Heat still have the best core in the league. Barring career altering injuries to their Big 3, it is inevitable that they will someday be a truly great team.
However, it was always silly to think that they'd be the best team in the league before they got a chance to really learn to play together and develop chemistry and without a good supporting cast. Give them another year or so together and get them a real starting point guard and center and a few impact players off the bench (e.g. Haslem) and they will be just as impressive as everybody thought they'd be.