First, give credit to the Pacers. The league's best defensive team figured out how to score on Miami early in the series, and pounded that method until the Heat figured out how to stop it. Roy Hibbert and Paul George are All-Stars at the beginning of what should be exemplary careers. George Hill and David West are really good players. Lance Stephenson had moments of excellence. Ian Mahinmi was doing things! It is certainly no shame to be tested by Indiana.
But the other piece of this equation is that actually achieving dynastic status is really, really hard. So much can go wrong. Like, whatever happened in the 2011 Finals, or Dwyane Wade's current injury. The San Antonio Spurs know this as well as anyone: despite a crazy run of excellence, they've never won back-to-back titles. Injuries, the Lakers and sundry other things have tripped them up in every repeat attempt. If you consider the definition of a sports dynasty as something like "protracted hegemony," then the Spurs have never really had one. (I subscribe to the common belief that three titles in a row is rare enough and awe-inspiring enough to be a dynasty.)
Consider the NBA's last dynasty, the 2000-2002 L.A. Lakers. The first title team of the Shaq-Kobe-Phil era needed a full five games to dispatch the upstart Kings in the first round, then conceded a 3-1 series lead in the Western Conference Finals to Portland and trailed the Blazers by 15 late in Game 7 before squeaking out the win.
The 2001 Lakers were widely considered to be saving their energy for the postseason; no title team has had a worse defense (No. 21 in the league) in decades. But the plot worked: the 56-win team went 15-1 in the playoffs to take the championship. That didn't look terribly likely in the regular season.
The third title team in 2002 needed 27 free throws in the fourth quarter of an elimination game against the Kings (Game 6) to stay alive, and only won that Western Conference Finals series when the Kings imploded in crunch time and overtime of Game 7 in Sacramento.
So, of the three straight championship teams L.A. produced, two were on the ropes of a Game 7 before making it to the Finals. I think we can excuse the Heat being pushed by the Pacers when we consider the overall greatness of the Miami team.
In other adventures in "finding dynasties that almost didn't happen," the 1992 Bulls needed seven games in the second round to survive and win their second title. The final Bulls title team in 1998 needed seven to survive the Pacers in the East finals.
The Heat have a huge test ahead in the Finals, and have to do it all over again next year to get that vaunted three-peat and the dynasty tag. As we've seen, a lot can potentially get in the way, no matter how talented your roster happens to be. That's what makes the designation special: it's really hard for even the best teams to accomplish.