The difference in the final game was 3 pointers: Cavs scored 9 more 3 pointers than Celtics for 27 pts. That's close to what they lost the game by.
IT had to be a difference. I understand he was playing hurt the first two games, and it wasn't made public. Without IT, the offense was too one-sided in Cavs favor. Take LeBron away from the Cavs, and they would have a tough time winning.
The other difference is their D in the paint sucks. Danny knows that, and he will take care of that this summer. He paid the price for not doing it the trade deadline this year, but I don't think he figured they'd get this far and he didn't want to mess up his cap space.
Hopefully, we'll see a better team in the fall.