Doc was spot on. From a competitive point of view, what Durant did was embarrassing. The same can be said for the Miami Heat, when LeBron and Bosh joined Wade. To me, free agents forming super teams like this for the sole purpose of winning the title, just cheapens the accomplishment of the championship. In no way should the 2008 Celtics be talked about in the same story. Danny had to actually trade valuable picks and players to get Allen and Garnett. BTW, Allen and Garnett were past their primes when they were traded to the Celtics, where as Durant, LeBron, Bosh and Wade were in the primes of their careers when they joined with their super teams.
Both Miami and Golden State had to make a lot of moves to free up cap space, including letting valuable players go (and some draft picks). Something feels a little better about making a real trade, but it isn't like those teams just signed these players to minimum contracts and didn't have to make sacrifices.
I mean obviously it was worth it for the Warriors to sacrifice Barnes, Bogut, Barbosa, Speights, and Ezeli to sign Durant, but that was 2 starters and a number of key bench contributors to free up enough room to sign him. He didn't just walk through the door and sign with the same team because that just didn't happen (the same core, sure, but not the same team).
Miami had planned for that off season for three years. They gave up a lot of victories along the way to make sure they had enough room for 3 max level players and then still had to make even more salary dumping trades that summer (like Cook + a 1st for a 2nd rounder, Beasley for a couple of 2nd rounders, etc.). Even then they still had to do sign and trades to make it work giving up multiple 1st round picks in that process.
The Celtics actually gave up real assets though. None of the players you mentioned for the Warriors or Heat really had great value. For the Warriors you are talking about a bunch of garbage and Barnes (which is what any team does when they do any upgrade let the old player they had at the same position go).
Bogut is ok, but he is too old now and can't stay healthy. He was bought out by the team they traded him for during the season. No team is going to count him as a starter moving forward.
Speights is at best a backup and is a dime a dozen.
Ezeli is damaged goods and who knows if he will ever play again. He did not play at all last season.
Barbosa is 34 and played 14 minutes a game on a rebuilding team.
This really was 100% about a cap spike loophole and nothing else. I think half those players would have been gone anyways even if they didn't sign Durant (Barnes would have obviously stayed, it is unclear what they would have done with Bogut).
The Heat is a little bit similar because I think they gave up the 5th pick as part of the Lebron Trade. However, Beasely was already seen as a bit of a bust (and a knuckle head) when he was trade so it really wasn't a big sacrifice to give up him and they immedately signed a bunch of vets to offset anything they had lost including Mike Miller.
So you compare that to what the Celtics gave up in their trades Delonte West (who was a legit combo guard before his issues derailed his career) the 5th overall pick, Szerbicak (a legit starter or high end bench player at that point in his career, different level than Speights or Barbosa). Then in the Timberwolves trade they gave up Jefferson (then viewed as a future all star), Gomes (nice young bench piece), Green (still believe to have some upside then) and 2 future first rounders. There really is no comparison between the 3 offseasons and what the teams gave up.
Also Cook never averaged more than 5.5 points after leaving Miami and out of the league by age 26. A truly bizarre player to bring up.