Yeah, chemistry and all that are great, but it doesn't make up for health or age.
Ubuntu didn't make Ray Allen older, so that he got blocked every time he went on a breakaway. Ubuntu didn't dislocate Rondo's arm so that he would spend half the series playing one armed. Ubuntu didn't make KG so old that he could only post up people once every other game.
Missed passes may stick in people's minds, but the difference is that the heat was far more athletic than the celtics, younger than the celtics, and had 2 guys who could score 30 a night if needed. How many breakaways did the celtics have where the heat caught up and blocked an easy lay up? How many breakaways did the heat have where they would finish the play before anyone from the celtics even made it to the 3 point line?
If anything, it was our chemistry and defensive cohesiveness that allowed the celtics to even be in most games, because physically, we were thoroughly outclassed.