Let's look at the Heat's competition:
The Spurs (who you derided for being "Old and Crappy") actually have way more young talent than the Heat. Ginobli and Duncan are 36 and 37 respectively, but Parker is 31 (same age as Wade, except he's not showing his age as much) and their games have never been based on pure athleticism like some other players. Their age still slows them down somewhat but they'll still be playing at a high level. But they have players like Cory Joseph (21 years old, defensive-minded PG who is basically at least as good as Norris Cole, except 3 years younger), Kawhi Leonard (22 years old, excellent SF who came into his own during the Finals and will get much, much better). Danny Green is better than any of the Heat's shooters (Battier, Allen-better pure shooter but not nearly as good defensively, Chalmers) and is only 26. Tiago Splitter is 28, same age as Lebron. Diaw is 31, younger than any of the Heat's bench role players. And while the Heat are not developing any young talent, the Spurs have consistently drafted and developed young players, stashing them overseas as necessary. Splitter was one of those, and I believe Ryan Richards will follow in his footsteps sooner rather than later. Overall, the Spurs are younger than the Heat. Who are you calling "old and crappy"?
The Pacers have young talent with Paul George (uber-talented, still improving. Probably will never be on the level of James or Durant but still very good). Roy Hibbert gave the Heat tons of problems in the playoffs because they have no one with his size. Granger didn't play at all in the playoffs against the Heat, but is a proven scorer when healthy. Stephenson is talented, a bit of a headcase at times but maturing. And he's young and improving his game. Very athletic without the greatest outside shot, I could see him as a poor man's Wade (and at this point in his career, Wade is also not what he once was, as I mentioned earlier). George Hill is a solid PG, not spectacular but neither is Chalmers. They've added some nice bench pieces in Scola and I'm a fan of Chris Copeland. David West is a great PF. Orlando Johnson could improve. Oh yeah, Scola is the oldest player on the roster and he's 33. That makes him younger than most of the Heat's bench. Which of these two teams will be better in three years, when Allen, Battier, Lewis, and Haslem retire and the Heat have no one to replace them with? I like the Pacers.
The Thunder have the greatest SF in the game not named Lebron James, and a player who is definitely of James' caliber. Kevin Durant is 4 years younger than James and has made great improvements in his efficiency, defense, and all-around game. Russell Westbrook is an outstanding athlete who is capable of being a #1 option on most teams, and seems determined to be the #1 option on the Thunder (and Durant lets him for some reason, but that's another story). Ibaka is a young big man, outstanding defensively, and improving his shooting. If he learns how to pass he'll be an offensive threat too. Collison picks up the slack for him though as an offensive big man. Reggie Jackson stepped up in the playoffs and looks to be emerging. Thabo Sefolosha is a nice "3 and D" player. They have tons of young talent like Daniel Orton (probably not going to amount to much, but has about as much chance of defying expectations as Oden), Jeremy Lamb, Perry Jones, and Steven Adams who can all become nice players in the future. In short, they have the pieces to compete now, and way more youth and upside than the Heat.
The Warriors and Nets both could be nuisances, but I don't think either has what it takes to be a legit contender. Don't completely count them out though.
I don't have time or knowledge to talk in depth about the Rockets now and there's a fair amount of uncertainty, but Harden is an elite scorer, Chandler Parsons may be the most cost-effective and underrrated player in the NBA IMO, Lin has been so