"Miami's team structure is flawed."
How many times have you heard someone say "the Heat don't have anyone except the Big Three!"? Or that they don't have a legit center, or that most of their bench is composed of three-point shooters who can do little more than just that? So called "true" NBA fans have been disgusted at the Heat's seemingly flawed team that somehow still manages to consistently beat teams with traditional squads.
LeBron James skill set fundamentally changed the NBA. Using him as a point forward in a small lineup allows for more flexibility on offense and and more quickness on defense. In a league where there are only a handful of elite centers walking around, Miami seems to have discovered a formula that just flat out works. It's hard to go against that.