To answer the question lets first point out what the Heat did, let’s say, insufficiently. The Heat only got 27 rebounds in Game 4 and got out rebounded by 17. The Heat shot 65% from the free throw line.
The Heat only scored 86 points on 45% shooting. If you remove Lebron’s 28 points on 10/17 shots (almost 59%), the rest of the Heat starters combine for 28 points on 32.4 percent shooting.
Most importantly, the Heat could not find an answer to the guard play of San Antonio; combined the Spurs’ guards shot 23 out of 36, 63.8 percent.
So how does Melo change any of that? For starters, Melo averaged 8.1 rebounds a game this season. 8.1 rebounds is more than any Heat player averaged in the season (Lebron 6.9) and in Game 4 last night (Lebron 8).
In 2014 Carmelo made nearly 85% of his free throws. In his career he is well over an 80% free throw shooter. That would make Melo the second or third best free throw shooter on the Heat behind Ray Allen and Norris Cole.
Carmelo Anthony is a proven scorer. The second best scorer on the Heat, Dwayne Wade, shot 1 for 10 in the first three quarters and finished the game with 3 of 13 shooting. Anthony would have provided an offensive boost that may have opened up passing lanes and opportunities for other players.
The solution to San Antonio’s guard play can be more scheme than defense. In Game 4 the Heat saw a steady diet of three guard schemes, pricking a weakness in the roster. With Carmelo on the Heat, Spoelstra could have switched to a three forward scheme of James, Bosh and Anthony.
That lineup would be unguardable by any three guard scheme in the league. In Game 4 a Melo, LeBron, Bosh lineup would be significantly longer than the Spurs’ three guard lineup and would force San Antonio to play more forwards and centers.
Would Melo have changed the outcome of Game 4? Who knows, but we may get to find out next year.