This Boston team just isn't an NBA Finals caliber team. They play reasonably hard and smart, but they just aren't one of the best teams in the NBA. This season is a once in a lifetime opportunity for the Celtics, because they will be lucky to get out of the first round next year when everyone in the league is healthy and rested after a full offseason for the first time in 3 years. The Celtics have to beat Miami in game 7, because I don't think this Celtics team, as constituted, can win a title in a normal season, even with a few tweaks.
Heat, Bucks, 76ers, and probably the Nets were all better than the Celtics this season, but none of those teams were healthy in the playoffs. The Warriors are going to be tough in the next round, but they look tired and the Celtics have a shot against them.